[ Easy to Use with Detailed Manual ] Features include Monitor, Talk, VOX (Voice Operated Exchange), Group, and Calling function. Increase/lower volume too! This intercom system is easier to use than others with user-friendly multi-functions and included step-by-step instructions! [ Supported by Power Bank for Outdoor ] This device is compatible with Power Bank (5V 1A) making it easy to take these intercoms any place you want. Besides, it designed with back hole for wall mounting.