Wifi doorbell connects to network via wifi router.(15-30m)
Mobile devices include smartphone or tablet, could connect to the doorbell.
After the visitor rings, mobile devices coulde interact with doorbell via real time video and audio, unlock, take photos, take videos, and alarm.
Answer the doorbell by smartphone, when someone press the doorbell, unlock the door from your smartphone on APP.
Don't worry forget the your key, you can open the door by your smartphone.