Facial recognition tech that can alert watchers on their own and home in on subjects are already in wide use. In China, EVERY square inch is blanketed with them. On the streets, in subway mezzanines, airpoets, bus depots, high speed rail depots etc. A giant interface in a control room showing every single face walking past framed in green or yellow squares. Police officers and techs can simply reach up, hover near the area they want to zoom in on and enlarge areas with simple hand motions like a hologram. A red square means that the face is that of a fugitive or someone who is banned from the country. Over 300 different people, from fugitives wanted for a variety of crimes, to suspected scammers, political dissidents, and foreign missionaries wanted for distributing unauthorized Bibles had been caught in the last year alone in random places. A pedestrian underground street crossing in Shanghai, a bus station in Nanjing, and a fast food court at a mall in Shenzhen. The 360° capable cameras are everywhere, synced up to millions of terabytes of data from national security storage. It is terrifying regarding the capability and blanket coverage of this system in China.
And they've had "stalker" drones for a while now. They don't explode, but when the cameras on either the stationary pods or a patrol drone recognize the face of someone they want to detain and question, that drone will silently follow the mark, hovering far beyond perception. And if the person enters a bus or subway train or car, the drones know not to follow inside. Instead, they automatically relay the status back to the central control hub, and other drones in other areas go into standby. When the person of interest emerges from the car or the subway station in another area and their faces are picked up again on the nearest camera, another hovercraft begins the follow routine, just like that, until agents or policemen on the ground make contact with the person and they 'terminate' the hunt on their interface linked smartphones. Most of these actions are not arrest operations unless the marked person is a fugitive or deportation case, but intimidation and mind games. Playing peekaboo with someone who is spotted pushing the boundaries of what is acceptable, and reminding them that they are being watched...