Every high-crime neighborhood in Chicago is studded with cameras with flashing blue lights. The enclosures are hardened. Destruction of CPD cameras has not been a major issue in the city. If the city can keep cameras operational, they can keep acoustic sensors (smaller, no line-of-sight requirements) secure as well.
My guess (just a guess) is that the "criminals will destroy the sensors" concern is totally overblown.
I heard about pissed of people in the UK putting a tire over a speed / red light camera post and lighting it on fire. Tires are harder to extinguish than your typical fire and it's usually too late before it can be put out. Eventually it becomes unprofitable for the third party contractor to stay there and they start going away.
Well, my comment was specifically directed towards the idea of a UAV first responder system. It's not hard to imagine ways that the detection system itself can be hardened (or hidden).
My guess (just a guess) is that the "criminals will destroy the sensors" concern is totally overblown.