Electric watchdog notifies from incoming mail
Attaching an accelerometer to the underside of the lid of a mailbox, hooking up a microcontroller, an LED and a piezo buzzer can make a device that notifies from incoming mail. The microcontroller (ATtiny85) is programmed to read the data from the accelerometer (GY-61), and when a sudden change in acceleration (the mailman opening the lid) is detected, the piezo buzzer plays a series of beeps and the LED is turned on. The LED will remain on until the reset button is pressed.
The box is laser-cut plywood with a lid of translucent acrylic, which is ideal for this project, since the electronics inside cannot be seen through the lid, but the blue LED is still easily visible when lit.