Here is another doorbell that lets you find out when you have a guest on your smartphone. The mydbell doorbell system does not require an electrician. It has a range of 300 meters (between transmitter and gateway). The companion app works on iOS, Android, and Windows devices. You will be able to see when your bell has been rung and decide who should answer the door next.
The Mydbell system is currently getting funded on Kickstarter. More information is available on Kickstarter.