In recent months, masses of Hong Kong citizens have taken part in a remarkable wave of protests, known as the Water Revolution. Ignited by the Hong Kong government’s attempt to pass a bill that would have allowed extradition to mainland China, and later in response to police brutality and rights abuses, hundreds of thousands of protestors abruptly gathered in various parts of the city to rise up against the encroachment of the incumbent regime. Through novel uses of social media and mobile technology, they acted in concert to confront riot police in wildcat actions. In effect, they exhibit a contemporary type of smart mob, as digitally savvy citizens engage with each other in largely ad hoc and networked forms of pop-up protest. This article illustrates both the continuity and changes in the recent development of a nascent smart mob in Hong Kong. It fleshes out how its protest repertoires and movement objectives have emerged and evolved vis-à-vis state suppression in the global city of East Asia. With a focus on changing contours, this article brings to the fore the pragmatic and temporally emergent properties of the smart mob to consider the widespread and protracted movement in Hong Kong.