Wireless transmission, easy installation, ready to use after delivery. Adopt waterproof design to avoid corrosion from tea, oil and water during work. Built-in 300mAh large-capacity lithium battery, capable of 37 hours of standby. Super resistant and anti-fall. All internal circuits are reinforced and more stable against drops.Can be used with 16 receivers, no need to worry about insufficient occasions. Adaptive power supply: DC 12V/1A Charging current: 20-50mA Standby time: 200 hours Number of code pairing: 998 Prompt mode: buzzer/vibration/light Modulation mode: AM OOK Working frequency: 433.92MHZ Menu option:set prompt time:set buzzer speed Set base ID/set extension number:set switch vibration Transmission distance: 800 meters in open space Voltage:AC220V Plug Type:EU Plug,it applies to Indonesia, Germany, France, Spain, Italy and so on Note:Due to different production batches, there may be slight differences in products. Colour:Black Material:ABS Package Contents: 1 x Wireless Calling System 16 x Receiver Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.