Literally all the time.

Every major piece of tech in use by police domestically was built originally for military use. Every large police department in the US operates fixed-wing surveillance drones, stingrays/imsi-catchers, camera-based tracking systems, etc. All but the smallest departments receive tons of milsurp vehicles, weapons, and gear. Night vision and thermal imaging systems were military tech, and now they’re standard for police. CS gas was military gear (until it was banned under the Geneva Convention), and now it’s used exclusively by police.