●Adopting 433MHz public channel, with long distance and strong penetration (about 800-1000 meters in open space) ●18650 battery powered, low power consumption, long standby time ●Outdoor units can be charged with solar panels ●Charging base design for indoor unit, Type-C charging port, same type battery for indoor unit and outdoor unit. ●38 pieces of music, 4 levels adjustable volume ●Indicator light for low battery and charging state ●Two-way hands-free intercom ●433MHz wireless unlocking (this function requires an optional unlocking device) ●Remote key unlocking（optional） ●The outdoor unit has IP55 protection level ●Easy and convenient installation