A honking big chain suitable for a motorcycle or a bicycle that you really care about. It weights about 7 kgs, so most likely not for use on the go. I use it in the garage, along with a couple sturdy U-locks, to lock up my bike and a couple other bikes, all together. It's not super long, 120 cm, meaning <60 cm in a loop. Would be nice if Abus had them in a few different lengths, I'd like a longer one, but I make do well enough with the current length. One of the ends has a bigger round-shaped link, that the other end can pass through, and the lock captures just that end. The lock itself is big and heavy and supposedly very secure. Some advice: pass your chain through your bike's frame (top tube, seat tube or one or both rear seat stays), pass it through the rear wheel as well, and a sturdy immovable object (metal pipe, ground anchor), make sure the chain is rather tight (e.g. wrap it another turn around the frame if it's loose). It's good to arrange things in a way that the lock is in a really awkward position to lock. If it's an inconvenience for you to lock it with a key, it also create a huge inconvenience for picking the lock. I'd say both lock and chain would withstand physical attack with even a large bolt cutter, and the lock is allegedly quite resistant to picking. For thieves with a battery- or gas- powered angle grinder, unfortunately no lock and chain can offer much resistance, if the thieves have a few minutes time to work undisturbed, they would get your bike. However, unless the thieves are after your bike specifically, if your bike is well locked, and there are other bikes around that are locked not as well, they would go for the easier catch. When a bear is chasing you and your buddy, you don't have to outrun the bear, just your buddy. The best solution, for sure, is to keep your bike next to your bed, possibly chained to it. Second best solution is to have multiple layers of security - more than one lock, an alarm, video surveillance, bike insurance.