Keyfobs

Keyfob is a small electronic device used to control access to doors or vehicles without inserting a traditional key. Modern keyfobs are compact, battery-powered modules that may combine a remote-control transmitter with a passive or active transponder, enabling entry and sometimes ignition through radio signals.

Keyfobs come in several variants. Passive keyfobs draw energy from the reader to power the transponder, while active keyfobs carry their own battery. Smart key fobs add microprocessors and cryptographic features to perform authenticated access, authenticate with a system, and support features such as proximity sensing and encrypted communications.

Most keyfobs operate using radio frequency communication. In automotive and access-control contexts, nearby devices use short-range RF or near-field coupling. Common frequencies include low-frequency 125 kHz for simple proximity devices, high-frequency 13.56 MHz for contactless transponders, and higher-frequency bands such as 315, 433, 868, or 915 MHz for remote operations and rolling-code protocols.

Typical applications include vehicle remote keyless entry and ignition, building and gate access, hotel room access, and secure asset management. The devices are often paired with a reader at a door or vehicle, which authenticates the fob before granting entry or starting a system.

Security considerations include the risk of cloning, interception, or relay attacks. Countermeasures include rolling codes, mutual authentication, cryptographic keys, tamper resistance, and management of lost fobs. Privacy and loss/replacement costs are also considered in system design.