If you're always impatient for the mail to arrive, and need to know the moment it has been received then the following project by Instructables member 1Serg may solve your problem. His solution involves a small Arduino-compatible board inside the mailbox that detects if the mailbox door has been opened with a magnet and reed switch.
Once the door has been opened (and hopefully real mail inserted), this Arduino will send data to another which is inside the house via inexpensive RF data link modules. The receiver can then activate an LED or other device to get your attention. It's a neat solution to a common problem, and complete details to make your own can be found on the Instructable page. And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.
Need a small Arduino-compatible for use with your own projects? Then check out out our LeoStick. It's the Arduino Leonardo-compatible board that's cheaper and smaller than the original:
Apart from being one of the smallest Arduino-compatibles on the market with USB, it also has an onboard RGB LED and piezo which can be used a knock sensor and various tune and sound effects. Plus you can add extra circuitry with the matching protostick! For more information and to order, click here.