1[Wireless Intercom System] This intercom doorbell kit features one outdoor unit and two indoor units, enabling communication between them. The indoor units are capable of communicating with each other as well. 2[Multi Functional] With 15 selectable ringtone options and three adjustable volume levels, you can choose the ideal ringtone and volume according to your preferences and needs. 3[Extended Transmission Range] The wireless transmission distance can reach up to 200 meters in open areas, and 5 to 50 meters in the presence of obstacles, ensuring dependable communication. 4[Expandable Intercom System] This intercom doorbell system is expandable, allowing the addition of more indoor or outdoor units, compatible with nearly any installation. 5[Intelligent Power Saving] Featuring an intelligent power-saving chip, this two-way voice doorbell provides excellent battery life. After a complete charge, it can function for over six months under normal usage.