[AnarchismIsCool]

Depends on the system, any pulsed emission of sufficient strength should start triggering things as you can't know for sure what bands and systems are going to be used against you. I believe they usually have 'unknown' IDs for stuff that isn't in the threat database.

[willvarfar]

There is a story of a police speed camera catching a fast jet going around. The snopes debunking has some interesting technical details of why this is really unlikely https://www.snopes.com/fact-check/police-radar-missile/

But of course people have built nuclear reactors at home, so they could probably assemble a sufficiently powerful radar too.

Edit: didn't mean that people need to power homemade radars using homemade nuclear reactors! I'm sure that's not necessary :)