Power locks or electric locks allow the doors of a vehicle to be locked or unlocked automatically. A keyless entry remote control using a key fob can enable a user to activate the door locks from a short range outside the vehicle. The basic system components include: lock actuator, switches, wiring and a circuit breaker. Voltage is sent to the actuator by using a control switch which is connected to the 12 volt power source of the car through a circuit breaker.
In some cases a body controller is used in conjunction with the door lock system. The body controller can unlock and lock doors when a correct condition exist such as lock the doors after 2 minutes of driving. Most actuators are normally located below the door latch of the car or are manufactured as part of the door latch. When the door is unlocked the actuator is supplied with power which excites an electrical coil, electromagnetism supplies the force to actuate the door latch.
Some actuators are manufactured with an electric motor and a gear set is used to move a control rod to activate door lock. A series of gears act as a gear reduction to move a rack and pinion flat gear. The motor can be driven in both directions depending on the use of the switch to lock and unlock the door latch.
Source by: http://www.2carpros.com/how_does_it_work/power_locks.htm