300 meters wireless transmission: The wireless signal has strong penetration and stability, and it can cover most of the apartment, villa, yard, small office, etc. 58 ringtones and indicators LED: 55 melodies to choose from, volume adjustable on 5 levels, from 0 dB (mute) to 110 dB. The LED light flashes blue when receiving a signal, so those with earphones or hearing impaired won't miss visitors. Memory function and expandability: Intelligent memory function, after changing the battery or restarted the doorbell, the doorbell will remember the last selected melody and volume settings, so there is no need to reset it. Support to extend this series of doorbell receivers and transmitters, driveway sensors, motion detectors, etc. Longer battery life: The doorbell (transmitter) has a built-in 23V 12A alkaline battery with a lifespan of approximately 3 years. The doorbell (transmitter) can be used in an environment of -20C to 60C. Easy installation: the receiver can be plugged into the socket and used, the transmitter can be stuck to the wall with adhesive tape double-sided or screwed to the wall. Installation tools are included in the package. 24-month warranty and lifetime technical support, any broken parts support free replacement.