How many times a day does your front door open? Is is open now? When was it last opened? This project puts this information online in a formatt compatible with other apps. Can be used for a door, window, even the fridge. Could be connected to a camera to record if the door opens. Endless posibilietes.
After assembling the wiring load the code into the Particle Core web interface. The light should come on when the reed switch is open.