Interesting how you reframe that, because the police would absolutely need a warrant to put a GPS tracker in your car.
This kinda proves everyone's point about this sort of thing, an officer following you is clearly different from the omnipresent surveillance dragnet enabled by Flock cameras.
Well that's not the tradeoff. It's impossible for everyone against cameras to get their own police shadow everywhere. When it takes that much labor they are forced to keep the average amount of surveillance down to reasonable levels.
We could also talk about restricting that kind of surveillance without a warrant, and stuff, but it's such a smaller problem. I wish my biggest surveillance risk was police pouring money down the drain to follow me around.