NFC works over a few centimeters at 13.56 MHz, the same frequency as high-frequency RFID, but adds two-way communication and the ability of a phone to act as either reader or tag. In IoT it serves three roles: a passive tag on a product or asset that a phone can read, a configuration channel for devices with no screen, and a trigger for pairing over a longer-range radio.
The configuration role is the interesting one for device makers. Tapping a phone to a sensor can transfer Wi-Fi credentials or a Bluetooth Low Energy pairing key without typing, which makes commissioning faster and more secure because proximity itself is a form of authentication. The trade-offs are that range is deliberately tiny and every tag or chip adds a small cost and an antenna loop to the board.
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