Single beam photoelectric cells are typically used in lift doors. Breaking the light-beam re-opens the lift door to avoid hitting or causing injury the persons stepping in or out of the cabin. To make this system more effective 2 pair of photocells are used in most lift doors. This solution is one of the cheapest means of protection in lift doors.
Camera sensors detect people in lift cabins. This solution can be very useful in buildings where a high level of safety is important (banks, governement offices,etc.).
