[masraum]

I've gotten weak alerts from all sorts of vehicles, including a crappy old conversion van once. I think in some cases, it's a radar detector. Yes, I'm certain that some really bad radar detectors can actually emit rf. I used to work for a company that used satellite communications, and we had experienced it.

But in your case, my guess would be that they may have some sort of proximity alert system or something.

I don't think it has anything to do with law enforcement.