The 125kHz proximity technology has been around since 1990 – it’s basically a physical RFID chip and when you present it to an EMI field the antenna inside is excited and responds with a signal that is identified by the reader. There’s a 26-bit format, which comprises of a site/facility code and the card number – site code from 0-255 and card number from 0-65500 – which is 16,702,000 possible permutations. It works well, but in the face of modern computing power, it’s a vulnerable technology.