How do you stop a powered gate from closing?          

Safety devices fitted to automatic gates protect users and vehicles by detecting the proximity of a car or user to the automatic gate or detecting their presence using safety devices that react to contact with gate.

Typically this would include photocells and/or light curtains that stop the gate in the event that the beam is obstructed between the light transmitter and receiver; if a person or vehicle obstructs the beam, the gate should stop before any contact is made and remain immobilised until the obstruction is removed and possibly a further command is given. Other safety devices would typically be safety edges or inherent detection in the gates motors that detect contact with any vehicle or user. When activated, these safety devices are designed to stop the gate, reverse a short way and then immobilise the gate again until a further command is given either by a user or by the control system.