All radar detectors leak a signal called “lo” frequencies, or local oscillator. Radar Detector Detector devices are designed to detect these signals. The first such device was the VG-2 Interceptor, manufactured by Kustom Signals Inc. It was designed to look for the “lo” signal at 11.55 GHz and alert the officer when it senses the presence of a radar detector. But most manufacturers caught on to this quickly and simply changed the frequency their “lo” leaked.

In recent years, a newer technology called Spectre has entered the market from Australia. Since its original introduction, it has gone through several updates and is now marketed as the Spectre III and is marketed by Stalker Radar in the US. In all recent tests, no radar detector on the market was undetectable to this new RDD, and as they claim to be able to update their guns as needed, it’s doubtful anyone will ever be for very long.

If you drive an 18 wheeler, a radar detector’s performance against radar detector detectors (or RDD’s) is critical, because they’re illegal to use in all commercial vehicles in every state in the US (Federal Motor Carrier Safety Administration Regulation 392.71). For most everyone else, though, this feature is unimportant as radar detectors are LEGAL in every state in the US, except Virginia and the District of Columbia.