Bicycle lock

A bicycle lock is a security device used to deter bicycle theft, generally by fastening the bicycle to a fixed object, e.g., a bike rack.

An inherent challenge to bicycle theft prevention is wheels and bicycle seats (seatpost fastener) with a quick-release lever, making them detachable from the frame (on most but the most economical of bicycles). Unless both wheels and frame are secured, wheels can be removed separately. An optimal locking method will secure the frame as well as both wheels — either to a fixed object or to each other.

Locking devices vary in size and security; the most secure tending to be the largest, heaviest and least portable. Lesser equipment is used to deter attempts by less skilled and determined thieves. Thus like other security equipment, bicycle locks must compromise between security, portability and cost. Some are made of particularly expensive materials chosen for their acceptable strength and low density.

An alternate defense is the provision of bicycle lockers or a bike cage in which the whole bicycle is locked, but these are rare and uncommon in most countries. A bike locker is not a bicycle lock.