There are three methods by which an automatic door is activated. 1. A sensor detects traffic is approaching. Sensors for automatic doors are generally:

• A pressure sensor - e.g., a floor mat which reacts to the pressure of someone standing on it.
• infra-red curtain or beam which shines invisible light onto sensors; if someone or something blocks the beam the door will be open.
• A motion sensor which uses low-power microwave radar for the same purpose.
• An electronic sensor (e.g. based on infra red or radio waves) can be triggered by something that someone carries, or is installed inside a vehicle. These are popular for garage doors.
•  A switch is operated manually, perhaps after security checks. This can be a push button switch or a swipe card.
•  The user pushes, or pulls the door, once the door detects the movement it completes the open and close cycle. These are also known as power-assisted doors.

In addition to activation sensors, automatic doors are generally fitted with safety sensors. These are usually an infra-red curtain or beam, but can be a pressure mat fitted on the swing side of the door. The purpose of the safety sensor is to prevent the door from opening or slow its speed if an object is detected in its path whilst opening and to prevent the door closing or reactivate it if an object is detected in its path.