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.