One day I thought “Wouldn’t it be nice if I know if I have new letters without having to check the mailbox?” That’s how I came up with the idea to install a wireless sensor that will notify me when somebody leaves something from me in the mailbox, mailbox sensor . The idea itself it’s nothing new and it’s very common among Arduino enthusiasts. What I think is unique is the combination of tools I used (or at least I couldn’t find a similar solution to the setup I have). In this posts I will just describe the wireless mailbox sensor. It’s basically one home-made Arduino (you can see this post on how you can build your own one) with an Xbee Series 1 transmitter and a couple of sensors: A DFRobot DFR0028 Tilt Sensor and a Snap-Action switch (similar to this one). The tilt sensor will detect when a new letter arrives and it’s placed in the small cover of the mailbox. It will trigger when the mailbox lid is lifted. Originally I thought of having a light sensor in there, but it was just easier to have an on-off sensor because I only need to recognize these two states. The snap-action switch will detect when I open the mailbox with the key (to reset the detection) and it’s placed right where the lock mechanism is resting. The snap-action switch is normally closed and when I use the key and rotate the lock mechanism, the switch will open, thus triggering the sensor. Every time a sensor is triggered, the Arduino will send a message to the coordinator (i.e. another Arduino I have in my apartment also with an Xbee attached).