The chain lock: a very safe way to protect your bike against theft. To use as a separate lock but also as an extension of your ring lock, so you can secure your bike twice as good. A chain lock consists of links of hard steel that are almost impossible to cut, which makes this type of lock so safe. They are available in different lengths. are a bit heavier than a cable lock, but if you want to put your bike away safely you take those few grams extra for granted.