I have been looking at alternatives for entry-access mechanisms. Some things to be looked into include:
NFC (Near Field Communications)
- Arduino NFC Shield features a transceiver module, PN532, which handles wireless communication at 13.56MHz, this means that you can read and write a 13.56MHz tag with this shield or implement point to point (P2P) data exchange between the shield and a smart phone. There is an NFC Library using PN532 to read/write card and communicate with android.
- Tutorial for NFC Shield and NFC Module from ElecFreaks.
Also similar to the topic is the controls behind the scenes. It is possibly to turn an Arduino into a PLC, complete with PLC style enclosures and PLC style software:
ModBerry, a Raspberry Pi based controller, but being Linux based, not quite so deterministic as an Arduino based product.
Automation Direct: not really open source, but lots of automation stuff.
Other interesting bits:
2017/10/26: LORA Chat Box from Hack-A-Day - Decentralised LoRa based Chat firmware for ESP32 boards by Heltec (and clones)