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Which bicycle lock that is a combination lock (with a code instead of keys) is the most secure device available on the market?

Of course everything can be broken, and its only a matter of time, but for which combination lock the time to crack it by a potential thief is the highest, without using tools that a thief is very unlikely to use on the street.

Considering that price and weight are not an issue. The only absolute requirement is that its a keyless lock. Is there anything that has an exceptionally good proven track record, preferably something that is being sold for quite some time already with no major vulnerabilities found?


Clarification: as a lot of people instead of applying common sense, made fun of me and spammed the answers with useless non-information, let me define terms used in the question:

The term "price is not an issue" is to be understood as "Price of the lock up to a single fee of 200 EUR (approx. 250 USD) is acceptable.

The term "weight is not an issue" is to be understood as "Mass of the lock up to 3 kg (approx. 6.6 pounds) is acceptable.

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Are you concerned with the physical security of the lock, or with the security of the combination code? –  zenbike Apr 21 '12 at 17:53
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@zenbike: well, both equally - as the thief will probably attack the weakest point, so its no good having a physically strong lock if the thief can somehow feel or hear the most probable digit. And vice versa. –  miernik Apr 21 '12 at 18:12
    
Any sort of multi-wheel lock with only 3 wheels is quite insecure -- can be opened in the matter of maybe 3 minutes, simply by trying every combination. At the very least require a lock with 4 wheels -- stretches the time to try every combo out to tens of minutes. (But note that some 4-wheel locks can be easily "sensed" by someone familiar with the lock.) But no lock will protect more than a few minutes (often no more than a few seconds) against a well-prepared thief. –  Daniel R Hicks Apr 22 '12 at 0:19
    
maybe crypto.stackexchange.com is a more suitable place for this question :P –  Alessandro Cosentino Apr 22 '12 at 0:58
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@miernik - Is using two combination locks an option? –  Neil Fein Apr 22 '12 at 2:16
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4 Answers 4

I would say that you might have some luck pairing up an industrial level combination lock with a big security chain. I've actually been toying with the idea of making my own bike lock for quite a while. THe problem with the big chains as I shown is that they are really mostly way too long, making them heavier than necessary. I would think that 18 inches (or maybe even 12 inches) would be sufficient to get the lock around the frame and back tire and lock it to the bike rack. The security chains really are quite difficult to break, even with a big pair of bolt cutters, and there are shrouded padlocks which don't really provide any place where the bolt cutters could even be used.

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I think ABUS is one of the most respectable, perhaps THE most respectable bike-lock manufacturer around. They have even some numbered levels of protection, the higher the level the higher the protection, even agains powertools (because of special steel alloys, and such).

They have some combination padlocks, which seem very interesting. Take a look at these 4-digit (ten thousand possible combinations):

There are other options in their site, but I think these are the most robust combination ones.

EDIT: just to complement, I think combination locks are a good option for errands, but not for whole-day or part-day parking out of sight. I suppose the OP intends to do so, since he mentions "in the street" and "keyless".

For example, I use to go to the supermarket by bike, and I think a combination would probably demand time enough to open so that someone wouldn't risk an opportunistic theft.

Now for parking at, for example, a train station full of annonimous bikes (none of these parkings in my city, yet), I'd go with the keyed ones, no doubt. A combination one would be an invitation for the thief to earn a bike AND a keyless lock "combo".

As a final thought: does anyone go out without his own home keys? Would a lock key be too much to put together in the home keyring? Well, just a thought!

Hope this helps!

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Here is a guy opening the ABUS Bordo Combo 6100: youtube.com/watch?v=fJ6FH1dzYQc so I was looking for something better. He doesn't show how exactly he does it, but it seems he can. There must be something better, some manufacturer who can make a combination lock in which you can't feel nor hear the difference between digits. –  miernik Apr 22 '12 at 7:23
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I'll have to give some of these suggestions a try. I haven't yet found a bicycle combination lock that I wasn't able to figure out how to determine the combination to in less than a few minutes. I used to have my wife set them to random values, and I'd break them open for fun. –  Stephen Touset Apr 23 '12 at 14:41
    
@StephenTouset An important question: did you find the combination by sequentially trying out the numbers, or by "feeling" the internals and fine-tuning the most probable combination? For 3-digit ones, sequential guessing is relatively fast. –  heltonbiker Apr 23 '12 at 16:07
    
"Feeling", and 5-digit ones. –  Stephen Touset Apr 23 '12 at 16:09
    
I've always used a keyed lock and see no real point in a combo lock (especially since good ones are rare). A simple padlock and cable or chain is far more secure, and, if anything, less trouble to use. –  Daniel R Hicks Apr 23 '12 at 17:55
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Kryptonite sell this combination U-lock which they rate as 6/10 "Moderate Security".

KryptoLok Combo

enter image description here

It should be good enough for most circumstances.

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linuxsquirrel.livejournal.com/45571.html here a guy describes how easily he cracked it by "turning the rightmost cylinder notch by notch, pushing in at each stop". That's not good. –  miernik Apr 23 '12 at 14:06
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No combination lock provides a high enough level of protection to warrant being tested as a valid means of security. Speaking from experience, I have never seen one that a decent pair of bolt cutters couldn't get through in less than 15 seconds. I'm not a bike thief. I volunteer at a bike co-op that takes donated bikes and refurbishes them for sale; these often have old locks on the frame for which the combination has been forgotten.

You'll find some lock comparisons online where they test the security of different locks against one another. However, these generally focus on mid to high-range locks, which always have keys. There isn't much point testing out the low-end combo locks.

However, since you've said that price and weight aren't an issue, but that a combination and security are the most important features, I recommend you keep your bike in a large safe.

the only secure method to store a bicycle with a combination lock

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You make some good points here, and these are important issues to cover, but this doesn't really answer the question. Given that miernik wants to use a combination lock, I'm guessing that convenience is more important than security. What are the options, given those limitations? –  Neil Fein Apr 22 '12 at 2:16
    
@user973810: downvoted, because its a non-answer. Did the question ask whether combination locks where generally inferior to keyed locks? No. And instead of applying common sense you chose to be sarcastic, wasting readers time with non-information. –  miernik Apr 24 '12 at 10:02
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