With touch-access entry and locking systems, what happens if I leave my key in the car? Does this mean anyone can unlock the car and drive off?

The push-button remote keys of the previous generation relied on infrared signals. Currently, the technology of automotive "keyless" access systems are based on short-range radio signal, and the "key" serves as both a receiver and transmitter.

While some cars with keyless systems require a miniature button on the door handle to be depressed to lock/unlock, others use a capacitive discharge switch on the lever so that mere contact with the handle commands the system to lock/unlock the doors and boot.

The keyless systems perform locking and unlocking functions as long as the driver carries the "key" in his pocket and is in close proximity to the door handle.

Radio signal antennae around the car are configured to detect if the key is outside or inside the car. Therefore, ignition can only be activated once the key is detected to be in the car. This is necessary for several reasons.

Firstly, it prevents someone from creeping into your car while you are standing outside, starting the engine and driving off.

Be warned, however, that if the engine has not been switched off, the car can still be driven away even if the key is in your pocket and no matter how far you are from the car. A warning on the instrument panel indicates the key is not detected, but the car can be driven.

If you leave the key in the car, the antennae will pinpoint its location as being inside and allow engine-start. Conversely, the driver will not be able to activate the locks from outside the car, even if the engine has been turned off.

To answer your question, it is possible for someone to drive your car off if you had left the key in the car. This would also have been possible before "keyless" systems.