Description: This is a portable doorbell system for home,factory, hotel, market, and more. Built-inmicrophone 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 thecall button on outdoor unit, the indoor bell will ring immediately for reminding you. You canpress 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 intercomSimple and Elegant: Ultra mini size ensureperfect 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 4x AAA Batteries (NOT Included.) Input Interface MicroUSB WirelessFrequency 467.6375MHz Transmission Distance 200m 5~ 50m Working Time 4 monthsWorking Temperature -20~ 55 Size Approx. 100 * 60 * 16mm / 3.9 * 2.4 * 0.6inApprox.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 .