NFC is an emerging technology for transmitting data over short distances. Its most basic component is the Mode Switch, which detects other devices in reach and propagates the device’s own capabilities. As this part of the firmware will be always running there are special requirements: low power consumption to ensure a long uptime and fast responses to satisfy the user. Besides it has to handle the difficulties of supporting the many different standards to which NFC maintains compatibility. This paper analyses these requirements in detail and presents an implementation how to fulfill them.