Depending upon the detector detector, they either work poorly or wickedly well.
The original RDDs were VG2 units. They were so so at the time, crap now. The VG2s emmitted their own signal, which could be detected by the RD also (passport, whistler, plus a few others worked this way). So when the VG2 was detected, it shut down power to the RD and thus no leaky signal could get picked up by the cops. VG2s could detect the RDs long before the RD detected the VG2, but chances are that the RD shut down before the cop figured out which car it was in. A V1 could be detected within 50 or so feet. WHich means you had to drive by the cop.
Then Spectre showed up. The latest iteration of that detector detector finds everything except the Beltronics STi. Cops here in Ontario have them en masse and should you drive down a 4 series highway here with a detector (excluding the STi) you stand a reasonable chance of loosing it and getting a fine.
The good news is that there are very few speeding traps in Ontario. I can drive from Toronto to Ottawa (4hrs) and chances are very good that I will see none, for either direction of traffic. Which is why average speeds here are about 85mph on highways like the 401. Everyone drives that fast. The police however do pace quite a bit with their radars off.
The Beltronics STi's leakage is non existant, so they cant pick it up.
thx Bel