RPi NFC Secure Entry This is a tiny home made tool that just monitors the door, detects users, and sends alerts. In the future it might sound an audible alarm and take pictures, but I don't have the hardware to test it right now, so it is what it is. By default, RPi NFC Security uses GPIO 23 as the signal pin. Wiring is easy, so long as you have bits of wire, aluminum foil, and a ~10kOhm resistor for the pull-down. Looks like the following: POSTITIVE PIN +_______________DOOR SWITCH_ NEGATIVE PIN -__10kOhm_______DOOR SWITCH_| SIGNAL PIN O__________| RPi NFC Secure Entry is licensed under the GPLv3 and bundeled is nfcpy http://nfcpy.org/ is under the EUPL, copyright Stephen Tiedemann. Dependant on RPi.GPIO and the bundeled nfcpy library.