BLEKey is a Bluetooth Low Energy (BLE) enabled tap for the Wiegand protocol, which is the most widespread protocol for proximity card reader systems. BLEKey can be installed in a reader to passively sniff Wiegand data, and can emulate cards on that reader. All data can be offloaded to a phone with BLE support.
BLEKey requires a CR1632 battery (not included) to provide power.
Source and design files: https://github.com/linklayer/blekey