Bike security can be a problem in some areas.
Swimming pools, railway stations, universities etc are all common venues where bike thieves seem to do their best work. But it has been known for bikes to be stolen even when locked inside a locked security cage in a secured underground car park with CCTV! Although this sounds absurd, it is not a made up scenario and actually happened to an Ivanhoe Cycles customer a couple of years ago. So I guess first we must admit that there isn't a lock made that can guarantee your bike or part of it won't be stolen.
Steel sign posts have been removed from the ground to release a formerly secured bike. Entire bike racks with bikes attached have been loaded into trucks. Bike frames have been cut to release a bike for the valuable parts to be stripped off. And of course locks have been cut with boltcutters, saws and grinders. Frozen with nitrogen and smashed open. Jacked apart with car jacks. The ingenuity and desperation of some thieves is incredible and the best we can do as bike owners is to never assume our bike is safe. Never leave it unlocked and unattended. Never think it won't happen to you and never buy a lock based purely on price if you plan to lock up a bike that has real emotional or financial value.
Obviously locking your bike if it is to be left unattended is sound advice and it is equally advisable to choose a lock which is relevent to the value of your bike and the vulnerability of the areas you are likely to leave it.
Some bikes are pretty rough and ready and the owner wouldn't be all that distressed if it went missing. It would be more of an inconvenience than a burden. For bikes like this and depending upon the financial situation of the rider, a cheaper lock may suffice. A deterent to deter those "casual thieves" from nicking off with your bike.
Most locks are operated by keys but if you can't trust yourself with keys or can't be bothered with the hassle of carrying them around and forever worrying where they are, a combination lock might be the type of lock you need. These locks are usually available in the cable style and are re-settable meaning you can choose a combination of 4 numbers which are very familiar to you. An existing pin, your birth date, the last 4 numbers from your phone number, whatever numbers you are sure never to forget. Or keep the keys safe and be sure never to lose them, especially if your bike is locked up somewhere!
Just how much security you can expect from a lock can generally be assesed by two factors. How much it weighs and how much you paid for it.
Generally speaking the heavier a lock is the more secure it will be, so try to choose a lock that is suited to the types of places you are likely to leave your bike and take into account the value of your bike.
A light weight, cheaper lock you can presume to mean, is not a lock to use when you are parking your $5000 bike outside a railway station. It is a light, easy to carry lock, ideal for kids parking their bike in the rack at school, or when leaving your bike outside the shops or when down the park or at the coffee shop. A cheap bike left in a rack at school obviously won't warrant the same level of security as an expensive racer parked out the front of a railway station at night.
Somewhere in the middle ground are the bulkier cable locks and mid range shackle locks, that will require some serious effort to break into. Tough locks that will see off most thieves, and are sufficient for most situations, although you must use some caution and common sense when it comes to selecting a parking spot, the time of day, the length of stay etc. For even a previously discouraged crook might have his interest rekindled if he sees your bike still parked as it gets dark or if it is at the same spot every day.
If you have an irrevocable attachment to your bike for emotional reasons or because its loss is simply a cost you cannot possibly afford then there are only two options. 1/ The first is to purchase as good a lock as you can afford, and having considered all of the information written above, expect that it will never get stolen and be thankful if this is the case, but be philosophical should it get taken, that you had done your best. 2/ The other option is to never let it out of your sight.
We stock a wide range of locks. Cable and shackle. Key and combination. Light and heavy. Short and long. Cheap and expensive. Asian and european and we are happy to help you choose a lock that is right for you. But please don't blame us if your bike still gets stolen, because as mentioned above, where there is a will there is a way and some thieves are desperate and determined.