I have one and am quite pleased with it. Yes, it alerts you to police presence, but generally only Highway Patrol, since the BCT-7 picks up the signal put out by the mobil repeaters that most HP units use and lets you know that there is an cruiser within a 3 mile radius and yes it has actually worked and saved my hiney.
How it works: Mobil Repeaters are radio transmitters that allow HP officers to use their handhelds and transmit long distance. A standard handheld radio has a limited range but when used with a mobil repeater, which picks up the signal from the handheld and transmits it through the larger car radio, it's a non-issue. The way most mobil repeaters work, whenever a radio transmission goes between an officer and dispatch on a given channel, any officer in that area/district will hear the signal, provided his radio is on. The mobil repeaters heat up and they broadcast their signal. If the HP unit is within 3 miles of a BCT-7, it'll pick it up and alert you. While it gives no indication of where the officer is (it could be that cruiser you saw parked at the truckstop you just passed), it DOES allow you to be on alert, which is the best anti-speeding ticket weapon.
However, not all agencies use mobil repeaters so it's wise to listen to the vocal traffic and that can give you an idea of their location. If you hear a lot of plate call ins, there may be a speed trap ahead.
I generally have mine set to HP and only use the scanner on the open road. Most local police frequencies are too chatty with non-traffic related situations, although you can pick up on some interesting [censored] sometimes.
