From The RadioReference Wiki
BearTracker™ Warning System
A Uniden trademarked feature usable on a small number of scanning radio models. It is also known as Highway Patrol Scanning and Highway Patrol Alert.
Every 2 seconds, the scanner checks for activity on BearTracker Warning System frequencies for your state. The BearTracker Warning System frequencies includes frequencies used by ‘mobile extender’ radios as well as by car-to-car, aircraft-to-car, and other special-purpose frequencies. You receive an audible (beep tone) and visual (flashing Alert light) alert whenever you are within an approximate three-mile radius of Highway Patrol/State Police units using a mobile extender unit.
The first radio to receive this feature was the BCT2 in 19XX then the BCT7 which came out in 1994. Then the BCT10 in 1995, the BCT12 in 1996 and later the BCT8 in 2003. In 2006 the next radio to carry the feature is called the BCT15. And more recently the newer 2017 BearTracker 885 which is now part of a CB/SCANNER and still has mobile extender alert system. It also scans the newer digital systems including the newer P25 Phase 1 and Phase 2 system that a lot of highway patrol are now using. Also applies to the BCT15X.
The radio was preprogrammed to scan the highway patrol frequencies of the individual states. The frequencies that it would alert on were usually mobile extender frequencies or mobile repeater frequencies. These frequencies, while active, would usually indicate the presence of a Highway Patrol officer. Because the scanner tended to give the operator the location of a nearby officer many of the users thought of the unit as a form of radar detector. Hence the design of the BCT10 and the BCT12 units that did indeed look like a Radar detector.