mailboxes network
This instrucКартинки по запросу mailboxes networktable will show you how to make a web-connected home mailboxes network. Besides emailing you when your mailbox is opened, it will also signal a Raspberry Pi sitting in your house to play an audio announcement. There is also a web-accessible Android/iPhone interface for you to check what time mail was delivered, as well as display the battery voltage left on the sensor.
But this could also easily be used as a web-connected security system, one that both plays an audio alarm in your home and emails you when the someone breaks into your house.
Under normal use (a few door openings per day), mailboxes network the battery powered mailbox sensor alarm Arduino should last over a year on a set of 4xAA batteries...