“I 
put a SmartThings mailboxsensor.com Multipurpose Sensor on my mailbox that tells me when the mail arrives.”“Did the mail come?” “Uh, maybe? I’ll go check. Nope.” This solution has worked as long as the postal service has existed, but we think there’s a smarter way. Use the SmartThings app and a Multipurpose Sensor to banish the guessing game for good.Use the “Add Device” feature in the SmartThings app to pair a SmartThings Multipurpose Sensor with your SmartThings Hub.
Place the SmartThings Multipurpose Sensor on the inside door of your mailbox to act as an open/close sensor. Use the “Smart Home Monitor-Custom” wireless mailbox sensor SmartApp in the Marketplace section of the SmartThings app to configure your Multipurpose Sensor to alert you when the mailbox is opened. I know it sounds nuts, but I have actually gone through the trouble of drilling through my mailbox and I have a wire that runs from the mailbox to my house. My original plan was to use a Raspberry Pi to notify me. That is before I got into z-wave and Smart Things. Given I have the wire running, could I connect a wired sensor (I was thinking a tilt switch) on one end and on the other end have a door switch with external inputs to notify me of the mailbox being opened?This instructable will show you how to make a web-connected mailbox sensor. 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), the battery powered mailbox Arduino should last over a year on a set of 4xAA batteries. The transceiver has a range of over 700 feet through multiple walls, so this should work for most situations.General Components:One strip board Arduino, circuit optimized for low battery power consumption
Strip board components mailboxsensor.com (voltage regulator, capacitor, resistors, etc…), see details later on.
Two wireless transceivers (RFM69HW)Two Arduino Uno’s with selectable 3.3V/5V switch for the gateways
One Raspberry Pi, but could be replaced with your PC/Mac if you don’t mind running the computer 24/7