Door sensors (sometimes known as photoelectric or infrared beam, electric safety door edges, door detector, electric proximity edges. or electric doorman) is an elevator device that detects a passenger or an object on the doorway which prevents the doors from closing (usually installed for accessibility). If a person or an object blocks the doorway and the sensors detects the person or object, the door will reopen then stays open and will not closed until the person moves away or the object is removed from the doorway. If the doors are being held open for a more than the specified period, the elevator will go into nudge mode and the doors will close slowly with a continuously beep. The door sensors will not work on the fire service mode, hence the fireman's elevator still need mechanical safety edges when the sensor not working. Door sensors are also possible to detect an object or obstacle blocking the doorway.