SmartBell lets you answer the door from anywhere in world
https://gadgetsfreeak.blogspot.com/2014/08/smartbell-lets-you-answer-door-from.html
A 23 Year old british student Daniel McGrane has made a Smart Bell, which will help you to respond to the persons outside your home, with your Smartphone, doesn't matter, where you are, inside home or at office or travelling around. Smartbell connects your door bell with your smartphone. So it doesn't matter where you are, if you wish you can respond to the visitor with you phone, just you need to be On Network!
So with the SmartBell, you can see who is outside your home, without leaving the comfort of Sofa, and you can leave pre-recorded message if you don't want to get disturbed. You can instruct the courier boy just sitting from the office is no one is at home!