Together with the lower part of the key, the hand-held radio transmitter forms one unit to function as the ignition key for the vehicle in question. This lower part of the key houses the immobiliser transponder and the key bit. The vehicle can be opened mechanically with this key bit by using the door lock and it can also be started with the key bit via the ignition lock. The integrated transponder is required in order to deactivate the immobiliser before starting the engine.
The hand-held radio transmitter, which is also called the transmitting unit or radio element, serves the purpose of locking and unlocking the vehicle doors via the central locking system.
Depending on the vehicle model or on the country of registration, the design and the functions of the hand-held radio transmitter can vary.
In the case of European vehicles, hand-held radio transmitters normally use a frequency of 433 MHz or 434 MHz. On the American and the Asian markets the frequency 315 MHz is used.
A red emergency button integrated in the side of the housing can be used optionally but is country-specific. When this red button is operated, an acoustic and visible alarm is triggered on the vehicle, a feature which can be helpful in an emergency situation or also when trying to locate the vehicle in confusingly laid-out car parks.