For commercial buildings, offices, medical practices, schools and large residential buildings. The entrance door is automatically unlocked electrically at certain times during the day. Visitors can come and go as they please. It is controlled by a timer. According to the switching times set on the timer, the door opener is constantly unlocked by continuous current (DC operation, no humming noise can be heard from the door opener). Outside of these switching times, normal door opener function, i.e. the door opener is released via the door opener button in the apartment (AC operation, a humming noise can be heard from the door opener).|A complete system consists of the following individual components: electric door opener, switching device, timer, transformer rectifier device, door opener button.|Door opener: Always use a door opener with 100% duty cycle. E.g. model 118---------A71 (12V 100%ED) or 118---------B71 (24V 100%ED)