It's an outdoor box designed for Rc522 NFC receiver. You can get the receiver on that link: https://www.ebay.com/itm/1PCS-RC522-13-56Mhz-RFID-Module-for-Arduino-and-Raspberry-pi-NEW-Z3/261976533776?epid=1278301906&hash=item3cff04ab10:g:orgAAOSwu4BVrwG7 and if you choose an othe modell you can cut off two holding leg and it will fit in the box. There is a hole for a 3mm indicator LED in the midle of the key sign.