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Criminology and Criminal
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The online version of this article can be found at:
DOI: 10.1177/1748895810392190
2011 11: 21Criminology and Criminal Justice
Graham Farrell, Andromachi Tseloni and Nick Tilley
The effectiveness of vehicle security devices and their role in the crime drop
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Article
The effectiveness of vehicle
security devices and their
role in the crime drop
Graham Farrell1
Simon Fraser University, Canada, and Loughborough University, UK
Andromachi Tseloni
Nottingham Trent University, UK
Nick Tilley
University College London, UK
Abstract
Car theft in the UK fell two-thirds from the mid-1990s as part of more widespread crime
drops, and has been attributed to improved vehicle security. This study develops a Security
Impact Assessment Tool (SIAT) to gauge the contribution of individual security devices and their
combination. The metric of impact derived is termed the Security Protection Factor (SPF). Cars
with central locking plus an electronic immobilizer, and often an alarm, are found to be ‘SPF 25’,
that is, they were up to 25 times less likely to be stolen than those without security. That impact
is greater than expected from the individual contributions of those devices, and is attributed to
interaction effects. Tracking devices are found to be particularly effective but rarer. Protective
effects were greater against theft of cars than against theft from cars or attempts, almost certainly
reflecting the difficulty imposed on thieves by electronic immobilizers. It is suggested that this
type of analysis could be usefully extended to other crime types and security combinations. The
analysis also lends support to a ‘security hypothesis’ component of an explanation for the major
national and international crime drops that is based in the criminologies of everyday life.
Keywords
British Crime Survey, crime drop, security hypothesis, vehicle security, vehicle theft
Corresponding author:
Graham Farrell, Institute for Canadian Urban Research Studies, School of Criminology, Simon Fraser University,
Burnaby V5A 1S6, Canada
email: gfarrell@sfu.ca
Criminology & Criminal Justice
11(1) 21–35
© The Author(s) 2011
Reprints and permission: sagepub.
co.uk/journalsPermissions.nav
DOI: 10.1177/1748895810392190
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22 Criminology & Criminal Justice 11(1)
Introduction
The most important criminological phenomena of recent times are the major drops in
crime experienced in many industrialized countries over the last two decades. Between
1995 and 2007 in England and Wales, violent crime fell 49 per cent, domestic burglary
58 per cent, other household theft 48 per cent, bicycle theft 20 per cent and other theft of
personal property 47 per cent according to the British Crime Survey (Hoare, 2009: 21).
These are the most substantial declines ever experienced in such crimes.
The UK experience parallels that of many, perhaps most, industrialized countries.
The crime drops were first observed in the United States where serious violent crime
including homicide fell by 40 per cent (Blumstein and Wallman, 2000, 2006; LaFree,
1999). With variation by country and crime type there were significant declines
across the 15 European countries for which reliable comparison could be made using
the International Crime Victims Survey (Van Dijk, 2006a, 2006b; Van Dijk et al., 2007).
Significant falls in crime have been identified in other countries including Australia,
Canada, Japan and elsewhere (see, for example, Rosenfeld, 2009; Rosenfeld and Messner,
2009; Tseloni et al., 2010; Zimring, 2007).
Amid the more general falls in crime, declines in vehicle theft were particularly pro-
nounced. In the United States, both the national police recorded crime data of the Uniform
Crime Reports and the National Crime Victims Survey data show that from 1991 to 2008
vehicle theft fell around 70 per cent. Between 1995 and 2008, vehicle-related theft in
England and Wales fell steadily and by two-thirds (65 per cent: Walker et al., 2009: 3).
The most prominent explanations for the crime drops offered to date are changes in:
demographics; sentencing and imprisonment practices; the extent and practice of polic-
ing; gun control and concealed weapons laws; teenage pregnancy and abortion; lead
pollution; crack cocaine markets; and economic strength. Yet despite a range of imagina-
tive research and innovative analyses, most of these ‘early’ hypotheses appear to have
little explanatory value. Some appear particular to the US experience, which differed
from other countries, including those relating to sentencing and imprisonment, policing,
gun control, abortion and the crack cocaine market (for recent reviews see Blumstein and
Rosenfeld, 2008; Farrell et al., 2010, in press).
The theoretical orientation for the present study is drawn from the ‘criminologies of
everyday life’ (Garland, 2000). The three prominent theories that we categorize as the
criminologies of everyday life are routine activity theory (see Felson and Boba, 2010),
crime pattern theory (see Brantingham and Brantingham, 2008) and rational choice
theory (see Cornish and Clarke, 2008). These interpret crime trends in terms of the
changing patterns of provocation and opportunity. Those patterns are a function of the
supply, distribution and movement of suitable targets, of guardians who might protect
those targets, and of those most likely to commit crime, all in the context of changes in
technologies and the built environment. Cohen and Felson (1979) use this basic, and
apparently rather simple, idea to explain the rise in crime in the United States follow-
ing the Second World War. The increased supply of suitable targets for crime (for
example easily removed cars and electronic goods), the decreased supply of some
forms of guardianship (for example with increased participation in the labour market
and hence reduced levels of day-time home occupancy) and the increased availability
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Farrell et al. 23
and movement of likely offenders (for example young men freed from domestic chores)
created a rapid rise in crime. None of the developments producing the rise in crime was
undesirable in itself. Increased criminal opportunities were a by-product of socio-eco-
nomic progress. The actual increase in crime spawned efforts to reduce it. Methods
focusing on opportunity reduction included efforts first, to reduce the suitability of
targets that would otherwise be attractive to likely offenders and second, to improve
guardianship where the supply of suitable targets was likely to be matched by a supply
of likely offenders. One possible explanation for the widespread crime drop is, thus,
that improvements in security have reduced opportunity. Just as routine activity theory
explained the rise in levels of volume crime (notably vehicle crime and burglary) after
the Second World War in terms of widening crime opportunities, so too perhaps the
recent falls in those crimes can be explained in terms of shrinking crime opportunities
effected by increases in security.
What we refer to as the ‘security hypothesis’ has been mooted by Clarke and Newman
(2006) and Van Dijk (2006b). Building on this, Farrell et al. (2008, in press) proposed
that change in the quality and quantity of security was a key driver of the crime drop by
reducing opportunities. Their work sought to explain trends in England and Wales, and
in Australia, and focused on vehicle theft and the role of security. In keeping with the
work of Brown (2004), Brown and Thomas (2003), Laycock (2004) and Webb (2005)
relating to England and Wales, and that of Kriven and Ziersch (2007) and Potter and
Thomas (2001) relating to Australia, the study concluded that better and more wide-
spread vehicle security underpinned the crime drops.
The present study complements those of Farrell et al. (2008, in press). It attempts more
precisely to identify the effectiveness of different car security devices and their combina-
tion. Furthering the understanding of the contributions from different devices, from their
combinations, and from them as a whole, is a means of drilling down into the details of
the causes of the most significant drops in car theft ever experienced. By looking in detail
at whether the form of opportunity reduction promised by a particular security device is
matched by detailed patterns of crime, greater confidence can be had that the device itself
is responsible for the reduced risk of crime. This is feasible because different security
devices work in different ways to reduce opportunities for different forms of crime, as
will become clearer as the article unfolds. Moreover, from a rather practical viewpoint
identifying the most effective single and/or in-combination car security measures may
direct the industry towards additional ‘crime-proofing’ of products and provide consum-
ers with information that empowers them to make more informed decisions.
In addition to the substantive contribution of this work we propose that the approach
should be replicable in other contexts, and so we term it a Security Impact Assessment
Tool (SIAT). The product of this tool is a metric of the effectiveness of security devices
relative to the absence of security, which we term the Security Protection Factor (SPF).
There is serendipitous correspondence with both the popular acronym and impact mea-
sure for sunscreen protection where the Sun Protection Factor is a metric of the protec-
tion conferred by sunscreen relative to its absence. In both cases the SPF states the
multiples of additional exposure time, relative to the absence of protection, beyond
which the average owner is burned.
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24 Criminology & Criminal Justice 11(1)
The next section gives a brief overview of key aspects of vehicle security to provide
context. Most of the remainder of the article is concerned with explaining the data and
the SIAT method, plus some interpretation of the SPFs.
Vehicle Security
Vehicle security is almost as old as the automobile itself. Newman (2004) provides a
fascinating account of the parallel evolution of car security and car safety. Many seem-
ingly everyday features such as keys and licence plates arose as early responses to theft.
Keys were an early immobilizer as they isolated the ignition system. Licence plates
reduced anonymity and allowed one stolen black Ford to be distinguished from the next.
Following the rapid rise in car ownership and theft in the 1950s and 1960s, mechanical
immobilizers (steering wheel and gear locks) showed some potential to reduce crime
(Mayhew, 1992; Mayhew et al., 1976; Webb, 1994). However, many mechanical immo-
bilizers could be overcome: one test found many could be overcome in seconds, and half
of them in three minutes and 20 seconds (BBC, 2000). Electronic immobilizers have
evolved as the preferred response. Good quality electronic immobilizers tend to be built-
in rather than retro-fitted and work by disconnecting one or more of the fuel, starter and
ignition systems (see Tilley et al., 2009). Likewise, door locks have evolved in form and
placement. Individual windowsill-top push-button door knobs have been displaced by
more discreetly located central-deadlocking with remote or proximity-activation by
increasingly encrypted radio-frequency identification (RFID) devices. Systems relating
to cars are now better regulated: the Vehicles (Crime) Act 2001 introduced the registra-
tion of motor salvage dealers and number plate suppliers and the Vehicle Identity Check
scheme, all aimed at targeting the re-selling of stolen vehicles.2 Licence-plate systems
are becoming more sophisticated to reduce false registration of stolen vehicles (Webb
et al., 2004). Southall and Ekblom (1985) dreamed of the crime-free car a quarter of a
century ago, and it seems that many of the measures they recommended have become
routinely incorporated during manufacture. In addition, although the present focus is on
devices fitted in vehicles, environmental influences upon car crime have also proved
amenable to prevention efforts. Work and leisure routines make car parks key nodes, but
risks can be reduced by quality surveillance, access control and other measures (Clarke
and Mayhew, 1998; Mayhew and Braun, 2004; Poyner, 1992; Webb et al., 1992; see also
http://www.saferparking.com). Car crime at residential nodes can be reduced by better
layout that facilitates surveillance by owners, particularly parking on driveways and in
garages (see, for example, Clarke and Harris, 1992). In recent years, automated number
plate recognition systems (ANPR) have sought to deny criminals the use of the road (see
Henderson et al., 2004).
Market imperfections mean little information on risk and protection was previously
available to consumers, so there was little incentive for manufacturers to develop security.
Hence car theft indices were developed to ‘name and shame’ manufacturers and alert
customers to the most stolen makes and models, those in the UK (Houghton, 1992;
Laycock, 2004) following those in the USA (Hazelbaker, 1997). Likewise, detailed
information derived from security tests by Thatcham (the Motor Insurance Repair
Research Centre) are now publicly available.3 Shaw and Pease (2010) have explored the
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Farrell et al. 25
potential to develop alternate measures akin to the theft index. They analyse information
from Motoring Which to determine whether vehicle security level informs the decision
of consumers to recommend purchase, and they include some examination of change
in security and its relationship to vehicle price. The importance of the Shaw and Pease
study lies in its recognition of the potential for publicly available market research data to
inform the development of novel market-based incentives for crime reduction. That is an
avenue worthy of further investigation but outside the remit of the present study.
It is clear that built-in and automated security has gradually changed the default in
recent years, from insecure to secure among many new vehicles. Time-delayed auto-
locking means the forgetfulness or apathy of car owners is now less likely to generate
easy criminal opportunities. This means, to adapt the insightful old pun, that the careless
are no longer the carless. At the same time, remaining thieves are faced with an increas-
ingly difficult task requiring extra time, skills and know-how, tools and other resources,
and risk.
Data
This study employs the British Crime Survey (BCS) data which were retrieved from the
UK Data Archive at the University of Essex. The BCS is a nationally representative
survey of adults 16 years or older living in private accommodation in England and Wales
(Bolling et al., 2008). It has been conducted since 1982, and annually with continuous
sampling since 2001. Data from the six contiguous annual surveys to 2007 are grouped
together here to increase the number of responses relating to the many combinations of
security devices. Data from both the Crime Prevention and Witness Intimidation Module C,
and from the Victim Module of the survey are used. In Module C, a randomly selected
sub-sample (one-fourth) is asked about the security measures relating to the main house-
hold car. Based on these answers we estimate the prevalence of car security devices in
the population of cars which is referred to herein as the fleet. In the Victim Module, victims
of car crime are asked about the security measures relating to their victimized car, the
prevalence of which we then compared to that of the fleet to generate our initial outcome
measure. We note at the outset that, in the BCS, the classification of ‘attempt’ does not
distinguish between attempted theft of car and attempted theft from car because of the
ambiguity of determining the aim of the offender when an attempt is thwarted.
The methodological limitations warrant acknowledgement. First, only those security
features recorded in the BCS can be examined. Second, the sample of main household
cars on which security information is collected is unlikely to be perfectly representative
of the population from which victimized cars are drawn because 41.2 per cent of house-
holds (in our merged 2001 to 2007 BCS file) had more than one car. We anticipate this
may over-estimate security effectiveness only slightly and would have little or no effect
on the between-device differences which are our main focus.4 Third, the car security
devices of the most vulnerable 1 per cent of the population are unknown. This is because
detailed information is only collected on the first three crime series per victim, and so it
is missing for about 1 per cent of the sample who experienced more than three. The BCS
survey strategy for victim module completion prioritizes personal over property victim-
izations. This means that when a respondent reports more than six series of crime
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26 Criminology & Criminal Justice 11(1)
(six being the maximum allowed, with a crime series being those of the same type that
the victim reports as being of a similar nature and committed by the same perpetra-
tors), car crimes are more likely to be excluded (Bolling et al., 2008). Hence in our
merged file, 9.8 per cent of thefts of car, 7.3 per cent of theft from cars and 5.2 per cent
of attempts lacked information on security devices.
The following analysis employs the data without weights. The incident weight adjusts
the sample-based crime rates to represent the population in England and Wales. In this
analysis however we do not have an estimate of the security features in the population of
cars, as discussed above, and therefore it would have been pointless to adjust the number
of victimized cars.
The BCS requested information on six main types of car security. These were central
locking, electronic immobilizers, car alarms, tracking devices, mechanical immobilizers
and window security etching. Information on whether devices were built-in or retro-
fitted was not requested in the BCS except for cars bought in the last five years. Likewise,
information on the technical specifics of individual devices was not available. It also
seems reasonable to expect that the quality of new devices has improved over time
(particularly electronic immobilizers) and that they have become more likely to be built-
in rather than retro-fitted – issues not addressed in the present study but which could
form part of future research. Such information might be available or inferred from data
on manufacturing or parts-sales, but identifying and collating such information was out-
side the scope of the present study.
Each of the six types of security device examined could be used alone or in combina-
tion with others, giving 64 possible configurations (including ‘no security’).5 However,
preliminary analysis suggested window etching conferred little additional security and
so it was not examined further, a finding that squares with that of Tilley et al. (2009).
The omission of window etching reduced the possible configurations to 32. In reality,
some combinations were more popular than others. Cars with electronic immobilizers
always had at least one other form of security. There were few cars with tracking
devices. These patterns probably reflect the more recent implementation of such devices
into the manufacturing stages of cars that already had other devices (alarms and/or
central locking). There were 31 configurations in the survey responses. However, there
were 13 categories which we categorized as minor because they each had only a small
number of cases (always less than 50) and accounted for only 150 cases in total. Findings
relating to the remaining 18 categories accounted for 22,616 cases, or 99.3 per cent of the
total, and are reported here.
Analysis: Developing the Security Impact Assessment Tool
The prevalence of security in the vehicle fleet relative to that for victimized cars consti-
tuted the initial outcome measure. In essence, the fleet measures the expected level of
security which, ceteris paribus, would be found among stolen cars. This can be com-
pared to the observed level of security among victimized cars. The proportions of each
were used to derive odds ratios. The odds ratio for each security combination could then
be compared to that for ‘no security’ to develop a score for the degree of protection
conferred.
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Farrell et al. 27
Table 1 shows counts of the number of survey responses for the 18 most popular
security configurations. A particular type of security is denoted by its capital first letter,
so that A is Alarms, C is Central Locking, E is Electronic immobilizer, M is Mechanical
immobilizer and T is a Tracking device. Multiple capital letters denote a configuration of
multiple devices, so that CE denotes cars with both central-locking and an electronic
immobilizer. The first numeric column of Table 1 relates to the fleet. Hence in the top left
numeric cell, there were 249 households where the main car had the four security types
constituting ACET. The second numeric column shows the number of stolen cars with
that security configuration. So, in the top row there were only three stolen cars which had
the ACET security configuration. The third and fourth columns show the corresponding
numbers for theft from cars and attempted theft.
For each security configuration, comparing the proportion of cars victimized relative
to the proportion of cars in the fleet, produces an odds ratio. Hence three of 1364 stolen
cars had ACET compared to 249 of 22,616 for the total population of cars with that
security combination. The odds ratio is calculated as (3/1364) / (249/22,616) = 0.2. The
set of odds ratios are shown in the last three columns of Table 1 for each crime type and
Table 1. Sample sizes and odds ratios by crime type and security configuration
Security
configuration
Number of respondents Odds ratio
Population Theft of Theft from Attempts Theft of Theft from Attempts
ACET 249 3 28 16 0.20*** 0.45*0.56**
CEM 1151 14 335 109 0.20 1.16** 0.83***
ACEM 3363 54 438 241 0.27*0.52*0.63*
ACE 5923 119 797 405 0.33*0.54*0.60*
ACM 1087 26 126 81 0.40*0.46*0.65*
CE 2074 54 541 219 0.43 1.04 0.92
ACEMT 168 5 23 11 0.49 0.55*0.57***
AEM 164 6 41 44 0.61*1.00 2.35*
EM 302 12 133 56 0.66*1.75*1.62*
AE 182 10 57 54 0.91*1.25 2.59*
CM 874 50 250 100 0.95 1.14*** 1.00
AC 1955 120 369 179 1.02** 0.75*0.80*
E 400 31 173 79 1.29*1.72*1.73*
AM 145 12 47 28 1.37** 1.29 1.69*
M 723 80 287 180 1.83*1.58*2.18*
C 2086 239 782 266 1.90 1.49*1.12***
A 240 60 117 68 4.15*1.94*2.48*
No security 1530 469 1133 450 5.08*2.95*2.57*
Total 22616 1364 5677 2586
Other 150 5 38 16
Don’t know 19 5 8 0
Key: A = Alarm; C = Central locking; E = Electronic immobilizer; M = Mechanical immobilizer; T = Tracking
device.
Notes:
(1) ‘Other’ = 13 minor security configurations (see text for explanation).
(2) Symbols refer to statistically significant difference in proportions (p-test):
*p-value ≤ .01; **.01 < p-value ≤ .05; ***.05 < p-value ≤ .10.
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28 Criminology & Criminal Justice 11(1)
security configuration. The odds ratios were complemented by a p-test for difference in
proportions. While the odds ratio shows the difference in the proportions, the p-test says
whether or not the difference was statistically significant (the three levels of significance
indicating the confidence held in that determination). The bulk of the findings did
show a statistically significant difference between security levels in victimized cars
and the fleet.
The security protection factor (SPF) shown in the first three columns of Table 2 is
derived from the odds ratios. The odds ratio for each individual security combination
was compared to that for ‘no security’. Hence the odds ratio of 0.2 for ACET was a mul-
tiple of 25.4 that of 5.08 for ‘no security’, that is, 5.08/0.2 = 25.4, our highest SPF. Tables
1 and 2 are ranked by the SPF for theft of car. Independent SPFs could not be calculated
for tracking devices, reflecting their rarity plus the fact that when they were used it was
always in combination with another type of security device.
In the final three columns of Table 2, a net interaction effect (NIE) is shown. This is
the difference between the expected and observed SPFs for security combinations. The
expected SPF is the sum of the independent SPFs of security devices when used alone.
For example, the independent SPFs for theft of car, at the bottom left of Table 2 are: A = 1.2,
C = 2.7, M = 2.8 and E = 4.0. Hence the expected car theft SPF for the AE configuration
is the sum of 1.2 for A plus 4.0 for E, a total of 5.2. This is compared to the observed
Table 2. Security Protection Factor and net interaction effect
Security
configuration
Security Protection Factor Net interaction effect
Theft of Theft from Attempts Theft of Theft from Attempts
ACET 25.4 6.6 4.6 17.6 1.4 -0.3
CEM 25.2 2.5 3.1 15.8 -3.0 -1.9
ACEM 19.1 5.7 4.1 8.5 -1.4 -1.9
ACE 15.3 5.5 4.3 7.4 0.3 -0.5
ACM 12.8 6.4 3.9 6.1 1.0 -0.6
CE 11.8 2.8 2.8 5.1 -0.8 -1.0
ACEMT 10.3 5.4 4.5 -0.3 -1.7 -1.5
AEM 8.4 3.0 1.1 0.4 -2.1 -2.6
EM 7.7 1.7 1.6 1.0 -1.9 -1.1
AE 5.6 2.4 1.0 0.4 -0.9 -1.5
CM 5.4 2.6 2.6 -0.1 -1.3 -0.9
AC 5.0 3.9 3.2 1.1 0.4 -0.1
E 4.0 1.7 1.5 - - -
AM 3.7 2.3 1.5 -0.3 -1.1 -0.7
M 2.8 1.9 1.2 - - -
C 2.7 2.0 2.3 - - -
A 1.2 1.5 1.0 - - -
No security 1.0 1.0 1.0 N/A N/A N/A
Key: A = Alarm; C = Central locking; E = Electronic immobilizer; M = Mechanical immobilizer; T = Tracking
device.
Notes: Results are based on the odds ratios of Table 1 and so that table’s statistical significance levels still apply.
N/A = not applicable.
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Farrell et al. 29
SPF of 5.6 for AE for theft of car, which is greater by 0.4. Hence 0.4 is its net interaction
effect. The net interaction effect gauges whether the effect of combining security devices
is the same, less or more, than the sum of the independent effects of those devices. For
the two security configurations involving tracking devices where an independent SPF
was not available (ACET and ACEMT), the NIE is based on the other devices in the
configuration as this seems preferable to excluding those configurations.
The NIE thus represents the additional SPF, or bonus, from the interaction effects
when security devices are combined. Negative NIEs should not be interpreted as sug-
gesting that those combinations did not confer additional security. A negative NIE gen-
erally means only that the total SPF was less than the sum of the individual SPFs,
though the total SPF is still greater than that of the individual devices.
Results
Different security devices would be expected to impact differentially by crime type.
Immobilizers would be expected to reduce risk of theft of cars because they make them
more difficult to drive away, with electronic devices being more effective than mechani-
cal ones. However, immobilizers would not be expected to generate much additional
prevention against theft from cars because they do not make it more difficult to break-in.
In contrast, alarms would be expected mainly to reduce theft from cars, although they
might also deter some more opportunistic thieves. Central dead-locks (central locking)
would be expected to reduce the risk of both theft of and theft from cars because they
make the car more difficult to enter. The results tend to support these broad
expectations.
For theft of car, central locking and electronic immobilizers featured in each of the top
four security configurations and in, respectively, seven and six of the top seven configura-
tions. There were no configurations involving both central locking and electronic immo-
bilizers that ranked lower than seventh. Alarms, central locking and either or both
immobilizers feature in the three security combinations with the highest significant SPFs.
For theft from cars, alarms and central locking featured in each of the six top security
configurations and in no other configuration. Alarms and central locking also featured in
the top five security configurations for attempted car theft. Tracking devices were present
in the most effective ACET combination, and while they remained rare in this sample,
they appear likely to play a significant role in the future of car crime prevention, a finding
that squares with those of Ayres and Levitt (1998) and Farrell et al. (in press).
Figure 1 presents the SPFs from Table 2 and facilitates easy visual identification of the
findings that: (1) crime prevention generally increases with the number of security devices;
(2) impact upon theft of car is greatest; (3) impact upon attempts are generally least; and
(4) the increase in protection is exponential in relation to theft of car. It also shows that in
the one instance where the SPF for theft from cars is greater, it relates to alarms.
Single security devices offered some protection but have relatively low SPFs. Alarms
on their own confer 20 per cent greater protection (SPF = 0.2) against theft of car and
50 per cent greater protection against theft from car relative to no security. The use of
only central locking (C) or only a mechanical immobilizer (M) approximately doubles
protection against theft of cars. The individual measure which on its own confers
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30 Criminology & Criminal Justice 11(1)
quadruple the level of protection against car theft is an electronic immobilizer (E), but
an electronic immobilizer’s effects against theft from cars and attempts are, as expected,
less marked than those of central locking.
Pairs of security devices generally produce significantly greater protection and in the
anticipated direction. Against car theft, pairs of devices are typically between four and
12 times better than nothing. Pairs generally confer greater protection against theft of
cars relative to theft from cars or attempted thefts. This is shown by the net interaction
effect values where four of the five pairs are positive for theft of car but only one for
theft from car and none of those for attempts. This measure suggests security pairs gen-
erally have an effect that is greater than additive against theft of car but not for the other
crime types. Central locking and electronic immobilizers are the most effective pairing
against theft of car (CE has SPF = 11.8 and NIE = 5.1). It is notable that the added
security from most pairs is less than additive for theft from cars and attempts (shown by
their negative NIEs). However, it is worth recalling that even when the NIE is negative,
the SPF of a combination of devices is generally still much higher than that of any of the
individual devices.
Security configuration triplets increase the overall level of security offered. Triplets
are most effective against theft of car where they are always at least eight times better
than nothing (SPF = 8.4 for AEM), and as much as 25 times greater. Although the SPF
25 for ACET and CEM is arguably the headline finding, it should be treated with cau-
tion because the odds ratio for CEM was not statistically significant and there is some
uncertainty over the SPF for ACET due to the inclusion of the tracking device. However,
ACE and ACEM have SPFs of 15 and 19, which appear to be reasonable minima for the
0
5
10
15
20
25
30
A
C
M
AM
E
AC
CM
AE
EM
AEM
ACEMT
CE
ACM
ACE
ACEM
CEM
ACET
Security Combination
Security Protection Factor
Attempts
Theft from
Theft of car
A = Alarm
C = Central locking
E = Electronic immobilizer
M = Mechanical immobilizer
Figure 1. Security Protection Factor conferred by security devices and their combinations.
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Farrell et al. 31
ACE combination against car theft. These configurations have NIEs that indicate bonus
security effects, perhaps due to the interaction of the devices, which are significantly
beyond additive.
A brief note is warranted on the possibility that improved car security caused crime to
displace to other forms of car crime or other crime types. We know of no evidence to sug-
gest that it did. As noted in the introduction, most crime types measured by the BCS fell
sharply from the mid-1990s. The parallel steep declines in each of theft of, theft from and
attempts, suggest there was no significant displacement within these types of car crimes.
Elsewhere, we have suggested that any increase in theft of car keys to steal cars has been
negligible within the overall picture of declining car theft (see Farrell et al., in press).
Conclusion
We offer conclusions in five areas:
1. Tracking devices appear highly effective but were relatively rare in the present
dataset. Among the more popular devices about which conclusions can be drawn
with greater confidence, electronic immobilizers were the most effective to prevent
car theft, and central locking the most effective against theft from cars and attempts.
Car alarms make a modest contribution to car security. Combinations of security
devices can confer greater safety. Central locking plus electronic immobilizers
confer significant security which is augmented by an alarm. Interaction effects are
apparent. Cars with this combination of security were 25 times less likely to be
stolen than cars without security, which is far above what would be expected from
the devices individually. The conclusion we draw is that all new cars – as many
already are – should be built with a minimal security configuration of central-
deadlocking, an electronic immobilizer, and an alarm system. Each system should
meet minimum standards, as they are already required to do in the EU, Australia
and many other countries.
2. This study suggests additional avenues for research on vehicle theft. There is a
need to isolate any possible confounding effects, particularly any due to vehicle
age and vehicle lifestyle (such as its usual parking location). Vehicle age is likely
to be positively correlated with the quality and quantity of security, that is, newer
vehicles will tend to have more and better devices. The inclusion of vehicle age in
the questionnaire for the BCS car security module would facilitate that analysis.
3. This study has implications for research into how crime prevention tactics
work individually and in combination. Combinations of tactics are often used –
against household and commercial crime, for example – but their individual and
interaction effects are rarely distinguished. The possibility of teasing out such
interaction effects is an enticing one that warrants further research. The Security
Impact Assessment Tool and the metrics it produces, the Security Protection
Factor and the Net Interaction Effect, may assist in such endeavours.
4. The major drops in crime that were experienced in the UK and elsewhere from
the 1990s were arguably the most important criminological phenomena of recent
times. Many types of crime in England and Wales were halved. Car theft fell by
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32 Criminology & Criminal Justice 11(1)
two-thirds and a range of studies suggests this is attributable to more and better
vehicle security. The present study has added to that body of work by teasing out
the relative contribution of individual security devices and their combination.
5. It took many years of rapidly increasing car crime, including much blood and tears
among the enormous social cost, before vehicle manufacturers adopted improved
security. Yet since they have done so, the crime reduction effect has been dramatic.
It seems reasonable to infer that, in relation to other crime types, manufacturers
and business should develop means to ensure that security is the default position,
at the very least to speed the pace at which crime prevention is developed and
introduced. Frequently stolen electronic devices such as MP3s, smartphones,
PDAs, laptops, SatNavs could almost certainly be built so that they could be
deactivated or tracked if stolen. This would mean theft would no longer be an
attractive option. Residential and commercial buildings and urban transport and
road systems should be designed in ways that overtly seek to minimize criminal
opportunities. It is clear that there is market failure when it comes to crime, and
that there is a critical role for government in nudging planners, manufacturers
and designers to improve security as an integral aspect of corporate social
responsibility.
Acknowledgements
We thank Jen Mailley for her contribution to the early stages of the BCS analysis. This work was
funded in part by Economic and Social Research Council grant RES-000-22-2386.
Notes
1. The authors are members of the Administrative Criminology Collective.
2. http://www.homeoffice.gov.uk/crime-victims/reducing-crime/vehicle-crime/.
3. http://www.thatcham.org.
4. For example, if main cars had as much as 10 per cent more effective security than non-main
cars, then our measure of security effectiveness would be an over-estimate by around 4 per
cent (slightly more because 6 per cent of households own three or more cars according
to the 2001 census findings. Available at: http://www.statistics.gov.uk/census2001/profiles/
commentaries/housing.asp (accessed 25 November 2009). But we anticipate that between-
devices differences in security effectiveness would remain only marginally affected if at all.
5. Six types of device with two possibilities (present or not) = 26 = 64.
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Biographies
Graham Farrell is a visiting professor at the Institute for Canadian Urban Research
Studies at Simon Fraser University, and professor of criminology at Loughborough
University. He has published on various aspects of situational crime prevention and
crime analysis.
Andromachi Tseloni is Professor of Criminology at Nottingham Trent University. She is
renowned for her work on individual, household and area predictors of victimization
frequency. Her research involves applying GLMMs and hierarchical models to predict
(entwined) social outcomes, with recent applications on crime perceptions, social capital
and crime drops.
Nick Tilley is a member of the Department of Security and Crime Science at UCL and
Emeritus Professor of Sociology at Nottingham Trent University. His research interests
lie in crime prevention, policing and programme evaluation methodology.
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