Warm tip: please do not put the transmitter installed on the metal door, because the metal absorption of radio frequency signals.
Specification :

Doorbell Button:
Weight: 65g
Frequency: 433.92MHz
Outdoor distance: >80 meters
Indoor distance: >30 meters (the wall)
Transmit power: 10dBm
Standby power consumption: 0W
Size: 83mm x 83mm x 8mm

Receiver:
Weight: 80g
Host power supply: AC 85-265V
Standby power consumption: 0.12W
Size: 83mm x 83mm x 21mm

Package includeds :

1 x Doorbell Button
1 x Receiver
1 x Set of Installation
1 x User Manual