Ha ha ha. It is the blind spot detection system. Even if turned "off," it still emits a signal.
See : http://www.valentine1.com/Lab/techreport3.asp
Disable K and X bands, and you're all set. In CA, the CHP and almost all local cops have switched to Ka (and laser), so you'll all avoid a buch of false positives. If you live in an area where cops still use those bands, you are kind of screwed.
Funny thing is that your car will also make OTHER people's detectors go off.