Wireless Voice Intercom Doorbell 2 Way Waterproof Home Security Access Control System Feature: 1. Intelligent and durable: mobile intercom, indoor machine has constant power, outdoor machine has long working time, intelligent pairing connection2. Adjustable volume: 15 bell chords, three levels of volume adjustment, the internal machine can be connected to each other, very safe3. Transmission distance: 200 meter long distance effective transmission, easily through four walls, receiver with flashing light reminder function4. Effective Waterproof: The waterproof design of the launcher complies with the IP44 waterproof standard and effectively prevents rainwater from entering5. Application Scenario: Wireless Voice Intercom Doorbell is widely used in home, office, laboratory environment, treatment, etc. Specification: Item Type: Wireless Voice Intercom Doorbell Material: ABS Battery: Internal Machine: 1 x 3.7V 890mAh Rechargeable Lithium Battery (Built-in) Outdoor machine: 3 x 1.5V AA battery (not included) Application: widely used in home, office, laboratory environment, medicine and so on Basic parameters: Radio frequency: approx. 410M - 490M Package list: 1 x indoor machine 1 x outdoor machine 1 x USB cable 1 x screwdriver 1 x user manual How to use: Install the battery and use.