Hands-free keyless entry badge detecting method for use inside vehicle, has four antennas within vehicle which transmit at low frequency but high amplitude and badges which signal identity and amplitude size received

摘要

A control unit (12) and four antennas (4) located within a vehicle (2) transmit at 125 kHz and a strength sufficient to give electromagnetic fields of 20nT in the cabin (6) and 20nT adjacent to the cabin (8). The badges used receive the signal and transmit at 433 MHz a return signal which identifies them and gives the strength of the received signal which enables the control unit to decide if they are in the cabin or not An Independent claim is included for a badge which can measure received signal strength, for use with the method of the invention.