Standard old Doppler radar units are INSTANT ON so the operator does not run emitting a detectible signal all the time. You watch traffic and when you see a fast car you hit the switch. Almost immediately you see a speed, as well as a corresponding SLOW DOWN if the driver has a detector. Or the frt end dipping when they hit the brakes.
The operator will use those observations in Court to show that in fact the car he had visually was THE car he was tracking on radar.
Radar detectors tend to NOT really work. UNLESS.....you can detect a signal AHEAD....then slow down. If You have no clue theres an Officer running radar, and speeding....and the Officer is a competant operator...Your toast.
I wrote quite a few people with high dollar radar detectors. And I'm sure many others got away if they were alerted by their detector of my radar unit. It's a gamble with a fairly highh downside for the driver.
Just did 4500 miles back and forth to the east coast. I rode 5-8 over the limit and got radar'ed several times. My speed was so low not worth the Troopers time. Would have been GREAT in the low traffic areas on I-94 to have gone 90-95..... but 80+ in a 75 mph zone was decent. Could be WAY worse...recall the idiotic 55 MPH National Speed limit days???
FN in MT