How do you stop an electric gate from closing?

NSI approved companies ensure that there are two different types of safety devices fitted to every automatic gate they install. Typically this would include photocells (magic eyes) and/or light curtains that stop the gate in the event that the beam is obstructed between the light transmitter and receiver. If an object, for example a person or vehicle, obstructs that signal, the safety procedure is activated. The other safety device would typically be pressure / safety edges fitted to detect any mass that might become trapped should the movement of the gate continue. When activated, they are designed to stop the gate, reverse a short way and then immobilise the gate again until a further signal to open or close is made.