Outdoor station:This door-intercom system impresses with its sophisticated, ultra thin design and excellent voice quality. This system is expandable to 4 outdoor and 4 indoor units. Regardless of the number of individual components you only need one power supply for powering the entire intercom. Address field and doorbell button of the stainless steel external station automatically light up with darkness.Indoor station:This door-intercom system impresses with its sophisticated, ultra thin design and excellent voice quality. This system is expandable to 4 outdoor and 4 indoor units. Regardless of the number of individual components you only need one power supply for powering the entire intercom. Address field and doorbell button of the stainless steel external station automatically light up with darkness.- Hands-free system- Continuously adjustable volume (language and ring tone)- Stop button turns off the ring tone - with visual display (e.g., with afternoon siesta)Door opener function