The trend as each new model of motor car is released is to fit more and more in the way of extra facilities. Most of these facilities involve electrically operating traditionally mechanical systems, such as windows, sunroof, door mirrors etc. However, technology is now such that these facilities, which were once found only in luxury cars, are fitted even on middle of the range models. One of the most useful facilities is central locking. The idea is that all doors, and sometimes boot (or trunk), are locked or unlocked automatically with the driver's door.
This is normally achieved with the use of switches and servo motors. A switch is fitted into the driver's door so that the action of locking or unlocking the door makes an electrical connection. This then passes a signal along wires which are concealed in the door panels and under trims to a servo motor on each door. Unlocking the driver's door will therefore drive each servo motor, which in turn drives a mechanical linkage unlocking all doors. The same principle also applies for locking. This system operates both by inserting and turning the key or by operating the lock/unlock plunger on each door. Many cars are now fitted with a safety switch (usually on the dashboard) which unlocks all doors, for example in the event of an accident. The obvious benefit in times of rising crime is that it is almost impossible to accidentally leave a door unlocked as long as the driver's door is locked.
