Feature: 1. Full Duplex Communication Mode: This wireless voice doorbell adopts full duplex communication mode, which is confidential to talk and anti interference. 2. Incoming Call Alert: This wireless voice doorbell adopts incoming flash light and ringtone alert, the alert time is 20 seconds, the incoming ringtone sound size is 108 decibels, which is bigger than the ringtone of cell phone, and the incoming call can be automatically answered. 3. Long Lasting: This wireless voice doorbell external unit has a normal working time of 6 months, with 5 presses a day and a 1 minute call each time. The inner unit plugs into 5V1A power adapter, and will never run out of power. 4. Wide Application: This wireless voice doorbell has a wide range of applications and can be used at home, hospitals, nursing centers, offices and so on. 5. Easy To Install: This wireless voice doorbell is very easy to install, the outer unit can be directly glued to the wall of the doorway, and the inner unit doesn't need to be installed. Specification: Item Type: Ultra Long Distance Wireless Voice Intercom Doorbell Model: H9 Material: ABS Battery: External Unit: Rechargeable Lithium Battery 3.7V 1000mAh ( With Built In Battery) Use: Widely used in home, office, laboratory environment, medical and etc. Basic Parameters: Operating Temperature: -20℃ ~ 55℃ Transmission Distance: In The Empty Space: Approx. 100m/328.1ft, Through The Wall: Approx. 5-20m/16.4-65.6ft Operating Frequency: 433MHz . Package List: 1 x Inner Machine1 x Outer Machine1 x USB Cable1 x Manual1 x Screwdriver