The secrets of keyless cars

Keyless ignition systems work on two levels. Firstly, the driver’s key fob is upgraded so it acts as a radio transceiver.This allows the fob to both transmit and receive radio signals, with each passing between the vehicle and the fob over a certain distance. Secondly, the vehicle itself is equipped with a series of internal and external antennas, which can likewise send and receive encrypted radio signals. The encryption, which is typically dynamic, prevents signals from being easily intercepted and used to gain illegal access. When the external antennas detect a key fob in close proximity, an encrypted radio signal is transmitted at a specifi c frequency (generally between 315 and 433 megahertz). If the fob, which is unique to each vehicle, receives the signal and returns the correct encrypted response, the car’s doors will unlock and engine systems will be primed. Once the driver gets in, the array of internal antennas sends another encrypted radio signal to the fob, querying it for a different response. If this is cleared, the immobiliser is turned off and an ‘on’ button can be hit to start up the engine.