Keyless entry fobs have been targeted by thieves with relay box equipment, used to extend the signal from fobs in homes to unlock and start vehicles parked outside.

A new motion sensor inside the Ford fob detects when it has been stationary for longer than 40 seconds and triggers a sleep mode, which will not respond to attempts to hack its signal via a relay box or through the misuse of other specialist equipment.

Moving the keyless fob by picking it up inside the home and taking it to the car will restore full functionality by the time Fiesta and Focus drivers approach their cars.

Ford fobs are designed to operate only within a two-metre radius of the cars they are bonded to.

Simon Hurr, Ford security specialist, said: “The online availability of devices which have no place in public hands has long been a problem for Ford, our industry and crime fighters. We are pleased to respond with a simple but effective solution – swiftly implemented to help protect owners of our top-selling cars.”