Description: This is a portable doorbell system for home, factory, hotel, market, and more. Built-in microphone and speaker allow super sound quality for dual way communication. Simple and small design, easy to use. Features: 2.4GHz signal ensures stable and smooth transmission. The effective transmission distance can be up to 200 meters. Dual-Way Intercom: When someone press the call button on outdoor unit, the indoor bell will ring immediately for reminding you. You can press the response button to talk with the people outside. Built-in high sensitivity microphone and speaker, allow audio input and output, ensure clear and smooth sound effect in communication. The loudspeaker has big sound, adjustable volume size, and change the ring tone. The intercom has clear sound quality and can be used by mobile intercom Simple and Elegant: Ultra mini size ensure perfect portability and easy installation, small and nice, easy to install. Specifications: Indoor Machine Voltage Range: 5V USB Direct Power Supply Indoor Bell Outdoor Bell Power Supply 4 x AAA Batteries (NOT Included.) Input Interface Micro USB Wireless Frequency 467.6375MHz Transmission Distance 200m 5 ~ 50m Working Time 4 months Working Temperature -20 ~ 55 ℃ Size Approx. 100 * 60 * 16mm / 3.9 * 2.4 * 0.6in Approx. 100 * 60 * 16mm / 3.9 * 2.4 * 0.6in Package Size Approx. 170 * 120 * 25mm / 6.7 * 4.7 * 1.0in Package Weight 150g Package List: 1 * Indoor Bell 1 * Outdoor Bell 2 * Glue 1 * Screw Driver 1 * User Manual .