A valuable thing left outside
Once bicycles became affordable, they became targets. A bicycle was easy to ride away, valuable enough to resell and often left on a street or at a station. As soon as large numbers were in use, owners looked for ways to secure them. The history of the bicycle lock is a long contest between security measures and the tools and methods used against them.
This article describes the designs that appeared, not how to defeat them, and it makes no claim that any lock design is secure.
Early solutions
In the 1890s, when the cycling craze made bicycles common, simple solutions were used. An owner could fasten the bicycle to a post or railing with a chain and an ordinary padlock, borrowing from techniques used for gates, animals and luggage. Some bicycles were also fitted with a small lock that held the front wheel or frame in a fixed position, making it harder to ride away.
Cycle clubs and some employers provided supervised storage, which is another form of security: a bicycle left with an attendant needed no lock. Such storage was particularly common in cities and at railway stations.
The ring lock
A form that is still common in the Netherlands and some other countries is the ring lock, a small lock fixed permanently to the frame near the rear wheel. When the key is turned, a bolt passes between the spokes, blocking the wheel. It is quick to use and always attached to the bicycle, though it can only prevent the bicycle from being ridden away, and a determined thief could still lift it. For that reason, many owners add a chain that attaches the bicycle to a fixed object. Ring locks are a good example of how local conditions can shape a design, since in places with large numbers of everyday bicycles, speed and convenience mattered most.
Chains and cables
The chain lock is one of the oldest designs. Chains are made of hardened steel links and are usually sold with a padlock or a built-in lock. Heavy chains resist cutting better than light ones but are difficult to carry. Their weight led to a market for lighter alternatives.
Cable locks, which use a flexible wire rope sometimes with a plastic covering, became popular because they are light and easy to loop through wheels and frames. The trade-off is that cables are generally easier to cut than hardened chains or U-shaped bars. Cable locks are therefore often described as deterrents for short stops rather than strong protection. Their development depended on wire drawing and rope-making techniques that had long been used in industry.
The U-lock
A significant change came in the 1970s with the spread of the U-lock, also called a D-lock. It is a rigid hardened-steel shackle shaped like a U, closed by a crossbar containing the lock. The shape leaves little space for tools to be inserted, and the stiff steel is harder to cut or pry than a chain or cable of the same weight. It became popular in cities in the United States and elsewhere, where bicycles were often locked outdoors.
U-locks led to a cycle of changes. Makers varied the thickness of the shackle, the shape of the crossbar and the design of the lock mechanism. Methods of attack were publicized, and manufacturers responded with new designs. Such back-and-forth has been a feature of the lock market ever since. Dates for early examples are not firmly documented in a single source, so the 1970s is best seen as the period when the design became widespread.
Folding and other designs
In the 2000s, folding locks appeared. They are made of hinged steel plates riveted together, which can be unfolded to make a loop and folded flat for carrying. They give some of the stiffness of a U-lock with more reach, though they are heavier than many cables. Other designs include armored cables, hardened chain sleeves in fabric covers and locks that attach to the frame.
Locking technology has often been paired with advice on technique, such as securing the frame as well as the wheels, but this article does not offer security advice.
Electronic and smart locks
Recent decades have added electronics. Some locks use alarms that sound if the bicycle is moved. Others use keypads, short-range phone links, cellular networks or fingerprint scanners instead of keys. Some devices combine a lock with a location tracker that uses GPS receivers or other signals to report where a bicycle has gone. These devices can give owners more information, but they depend on batteries and software, and their reliability varies. No electronic system makes theft impossible.
Beyond the lock
Registration schemes, frame marking and databases of serial numbers are also part of the history, since a stolen bicycle is easier to recover if it can be identified. Some cities have also introduced secure parking areas, which shift the problem from the individual lock to the infrastructure. Bicycle-sharing systems, with docking stations and electronic access, are a different approach, because the bicycles are owned by the operator and are not left to individual owners to secure.
A lasting pattern
The bicycle lock shows a pattern that appears in many security devices. Each new design leads to attempts to defeat it, which leads to improvements. The result is not a final solution but a series of trade-offs between weight, cost, convenience and strength.