Master intercom works with a door intercom (sold separately) to enable audio communication with visitors prior to granting access Door-release button controls an electric strike (sold separately) to remotely unlock the entrance for a visitor Works with any LE or LS Series door intercom (sold separately) Adjustable chime and audio volume Accepts additional Aiphone LEM-1DL master intercoms to extend door monitoring capability to other rooms within the building or into large areas