There are four types of bike locks: cable locks, folding locks (segments), chains and D-locks.

There are two main criteria when choosing a bike lock: the level of security (actual or perceived) and the fastening system. There are then criteria to consider for each type of lock: how easy it is to transport, how long it is, how flexible it is, how much space it takes up and how much it weighs.
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1. Safety Level

B’TWIN and the CNPP, an independent laboratory, have devised a test protocol for assessing how secure a bike lock is in real-life situations, on a scale from 1 to 10.

Bike locks with a score of between 1 and 4 are recommended for securing your accessories (helmet, basket, saddle, wheel).

Bike locks that score 5 or more are suitable for locking up your bike.

The higher the score, the better resistance the keyhole will have to lock picking and the better the body will withstand attacks by expert thieves with increasingly sophisticated tools.

No bike lock is unbreakable. Instead, they are intended to dissuade potential thieves from trying to steal the bike.
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2. The Fastening System

The differences between bike locks should not be taken lightly. They are not all designed in the same way, which is why they have different levels of protection.

Chain locks come with links of all shapes and sizes and different levels of security, allowing you to easily lock your bike to a fixed point, lock several bikes together, or attach your bike to its wheel. They also come in different lengths to suit your needs (locking several bikes together, for example).

Light, compact locks that are easy to carry. They are designed for securing your bike accessories (bag, basket, saddle, helmet, etc.) but aren't enough for your bike itself.

The go-to, high-security deterrent. They come in different sizes and are used to attach one or several bikes to a fixed point. They offer the same level of security as a chain, but are lighter and can be mounted on your bike.

Folding locks are more resistant, compact and easy to transport, with a higher level of security than cable locks.