An actuator is the mechanism that moves something under electrical control, such as a lock bolt, a damper, a valve or a gate arm. In security work it is the final step of a decision: the controller supplies power, the actuator moves, and the door, vent or barrier opens or closes.
Actuators are where electronics meet physical resistance. A camera observes and a controller decides, but an actuator is what actually changes the state of a building.
Where actuators appear
Electric strikes, magnetic locks, automatic door operators, turnstiles, gate arms and HVAC dampers all depend on one. Some are on or off devices; others, like valve and damper actuators, move to a position and hold it. The type decides the wiring and the power supply.
Power, torque and duty cycle
An actuator has to overcome real load: a stiff latch, a heavy gate, a spring-return damper. Its duty cycle limits how often it can cycle without overheating. Matching the device to the load, and leaving a manual release for maintenance, prevents the failure that appears months later.