Known as the Posto no Mihariban in Japan, all you have to do is set up the antenna and transmitter on the inside of the lid of your post box. When something is put inside by the mailman it sends out a signal to your receiver, connected up to 100m away in your home. Each signal clocks up a number on the receiver so you even know how many items have been delivered. If used ten times in a day the transmitter power will last some five months.
It's actually a keen idea, but poor execution in appearance and size. We'd love to see someone fashion something similar on a smaller scale and perhaps integrated with wi-fi notification to your Android or iPhone device.
Available for $92 from JapanTrendShop.com.