In plain English
NFC is the technology behind tap-to-pay and most modern access cards. In physical security, NFC enables staff to unlock doors by tapping a card, fob, or their smartphone against a reader. Because the range is extremely short (typically under 4 cm), accidental reads are rare. Modern access control platforms like Ubiquiti UniFi Access support NFC credentials via cards, key fobs, and mobile devices running iOS or Android.
Full definition
NFC operates at a range of roughly four centimetres, short enough that a tap is deliberate and accidental reads are uncommon. The technology underpins tap-to-pay at retail terminals and most modern workplace access cards. In a physical security system, an NFC reader mounted on a door frame checks the credential presented against an access control database and either opens the door or logs a denied attempt. The whole exchange takes under a second.
NFC credentials come in a few forms: plastic cards, key fobs, and mobile devices. Mobile NFC credentials are increasingly common because they can be provisioned and revoked remotely without the cost of reprinting cards. A staff member who loses their phone can have their mobile credential disabled before they reach the next door. That is meaningfully harder with a physical card, where the gap between loss and revocation is often measured in days, not minutes.
One limitation worth knowing: standard NFC cards can be cloned with equipment that costs very little and is freely available. High-security implementations use encrypted credentials, such as those supported by UniFi Access with mobile NFC or MIFARE DESFire cards, which are significantly harder to duplicate. For environments where or credential cloning is a real concern, pairing NFC access with a secondary control such as a PIN pad or video verification at entry points is the standard approach.