[Features] Working principle: The transmitter is installed outside the door, the receiver is installed on the power socket, press the transmitter to ring the bell, and the receiver immediately rings the bell and lights up to remind Plug and play without wiring: the outside transmitter is attached to the wall and the indoor receiver can be used after plugging in Strong penetrating power for long-distance transmission: strong signal penetrating power can be used in offices, office buildings, home stores, factories and other occasions Long-distance barrier-free 300-meter penetration Strong penetrating performance, the receiving distance from the open ground can reach 300 meters [product information] Name:doorbell set Color:black Product material:plastic Product size: 59*91mm 46*76mm Packing list (you can get after purchasing one item): 1*Transmitter + 1*Receiver Please understand: 1. Due to the long shipping time, the item may be damaged during the shipping process, if the item is damaged, please leave us a message through the official website immediately before posting comments, and I will solve the problem for you. 2. Due to manual measurement, the size may have an error of 1-3cm. 3. Colors may vary from monitor to monitor.