fobs

A fob, short for key fob in many contexts, is a small electronic device used to grant access to a secured object or space. Modern fobs typically communicate with a reader by radio frequency or magnetic induction, either by close proximity or by remote signaling. The term encompasses both car key fobs and access-control fobs used for buildings, offices, and hotels. The phrase originated from the decorative pocket-watch fobs that accompanied chains.

Car key fobs provide keyless entry and, in many models, push-button ignition. Building access fobs consist of RFID or NFC cards or fobs carried on key rings that unlock doors when presented to a reader. Hotel room keys and transit passes often use similar credential fobs.

Most fobs fall into passive or active categories. Passive fobs derive power from the reader's field (RFID or NFC) and do not require a battery, while active fobs contain their own power source. Automotive fobs commonly use cryptographic challenge-response protocols and rolling codes to prevent interception and replay.

Security and privacy concerns include skimming, relay attacks that extend the effective range of a fob, and loss or theft of credentials. Mitigations include deactivating lost fobs, implementing encryption, limiting operational range, and using multi-factor authentication for sensitive access.

Standards and practice vary by application; common technologies include ISO/IEC 14443 for contactless smart cards, ISO/IEC 15693 for vicinity cards, and various vendor-specific automotive protocols. The evolution continues toward hands-free operation, stronger cryptography, and integrated multi-credential platforms.