Here is a smart doorbell system that helps you catch your guests on your phone. The mydbell system lets you know as soon as a visitor rings your door. The companion app shows when your doorbell has been rung. The device has a range of 300m (between transmitter and gateway). It has single and voting modes.
This smart doorbell also lets you decide with your friends whose turn it is to answer the door. The mydbell app will be available for iOS and Android devices.