 Since the device is carried by the driver, usually in their wallet or pocket, if the driver leaves the immediate vicinity of the vehicle, so will the transponder, causing the system to assume the vehicle has been hijacked and disable it.As the transponder itself is concealed, the thief would not be aware that such a system is active on a vehicle until they had ejected the driver and moved the vehicle out of range of the driver (usually only a couple of meters).This is probably the most common anti-hijack system, and a central locking system that uses the same concept was demonstrated by Jeremy Clarkson on an old episode of the BBC Top Gear program where he teased a butler by asking him to put his bags in a Mercedes-Benz S600 but didn't give him the RFID transponder.