HE mailbox at my previous residence was down at the bottom of a long, steep driveway, very far from the house. Checking whether the mail had come was a long and tiring process, and if it turned out that it hadn't come yet or one my six roommates had picked it up already, it was very annoying. So I built the mailbox project. When there's mail in the box, it is detected by a light sensor, and a motor flips a flag up, which you can see from the house. When the mail is removed, the flag goes down. The contents of the mailbox were no longer a mystery.