Keyfob

A keyfob is a small, handheld electronic device used to control access to vehicles or buildings remotely. It typically contains a battery-powered radio transmitter and sometimes a passive transponder, and it communicates with a receiver in the target object via radio frequency or near-field technology. The term encompasses both active fobs that operate by emitting signals and passive fobs that are recognized when in proximity.

In automotive applications, key fobs enable functions such as locking and unlocking doors, opening the trunk, arming or disarming alarms, and, in many modern systems, starting the engine remotely or via a proximity-based push start. In building and facility access, key fobs usually use RFID or smart-card technology to grant entry when presented to a reader. Some fobs combine multiple functions, and many manufacturers now offer proximity or passive entry where the user need not press a button to gain access.

Security and privacy considerations are central to keyfob design. They commonly employ rolling codes, challenge-response authentication, or encryption to deter cloning and interception. Proximity-based systems can be vulnerable to relay or relay-like attacks if not properly protected. To mitigate risks, devices may include immobilizers, require phase-specific authentication, or allow deactivation of lost or stolen fobs. Battery replacement is a routine maintenance task for many fobs, with coin-cell batteries being typical; some models provide a mechanical key blade as a backup when power is depleted.

Historically, remote keyless entry devices began appearing in the 1980s and became widespread in vehicles during the late 20th century, with building access fobs growing in use in the following decades. The term “keyfob” reflects the original small decorative items attached to keys.