By emitting with enough power to be useful, you get into the range that you need to have a licence.
I think by "emmitting" Tocomment means "sending update to the server", thus notifying everyone who is connected and is in some certain range from the point.
No I domean emitting radar. Now a radar gun obvoisly doesn't need a license and that emits detectible radar.
To make my idea legal how about building a combination radar detector/radar gun. Officially the purspose of the radar gun is to get a second estimate on your speed when you may be in proximaty of a trap.
Sort of like Ethernet collisions? You notice a collision and start yelling "collision, collision" on the segment?
Make radar detectors emit radar when a trap is confirmed.
Use case: Radar detector alerts you to what it thinks is a trap. If it is a trap, you hit a button and it will emit radar for 5 or 10 seconds to warns approaching motorists? The bonus is all existing radar detectors can pick up the signal.