Doorbell, Wireless Doorbell Intercom Battery Powered 4900ft Long Range Waterproof 3 Volume Levels 20 Ringtones for House Classroom Business Office TWO-WAY COMMUNICATION: The doorbells work like intercoms.Unlimited number of indoor and outdoor machine connections.Indoor units can communicate with each other.Different sets work together. LONG RANGE: The range of the intercom doorbell is up to 4900ft/1500m in open areas.Stable signal and the call sound is clear with 3 different volume levels and 20 ringtones. EASY TO USE:This doorbell does not require Wi-Fi, Bluetooth or pairing with a mobile phone,only one button push to talk.It takes a 3 second power button push to turn them on or off. BUILT-IN RECHARGEABLE BATTERY: The outdoor unit can be used for about half a year on a full charge, and the indoor unit?7 days.The indoor unit comes with a charging base that automatically cuts off when fully charged. IP44 WATERPROOF:The operating temperature of the doorbell is -4?-140?, and the body is waterproof so it can be used outdoors even on rainy days Product Description ATTENTION: Can not start the conversation from inside unit!The outdoor unit must call the indoor unit first to start communication.The indoor unit and the indoor unit can call each other. The two units cannot hold down the TALK button to speak at the same time Outdoor unit Press and hold the TALK button to speak. The indoor unit can hear the voice in real time. Release the TALK button after speaking. When the indoor unit hears the end of the outdoor speaking, press and hold the TALK button to speak in response. Previous page Long Working Range The communication distance will be reduced if the units are blocked by walls (especially metal objects) and other environments. Please try to avoid unnecessary obstructions when using the device. Next page Adaptable to a wide range of environments Press the "Volume Button" to adjust the volume and Press "SET button" to adjust the ringtone. Built-in 1800 mAh rechargeable battery Please connect the power cord to the adapter, then connect it to the charging base and place the indoor or outdoor unit in the charging base. When charging, the red light is always on. When fully charged, the green light is always on. The indoor unit can be placed on the charging base continuously. Special secret key matching technology Attention:Microphone whistling when devices are too close together. Added audio interface for external sound ATTENTION:When shipped from the factory, the power of the indoor unit and outdoor unit is between 20%~30%, please fully charge them before using and installing.