The standard bike lock is a simple U-shaped piece of hardened steel with a locking cross piece. Hardened steel is tough to cut, but modern tools make this much less of a chore than it used to be. For example, a Chinesium angle grinder complete with cut off disk will get you through a lock in less than 5 minutes for <$40. If you want to avoid sparks and the need for mains electricity, then an electrohydraulic rebar cutter will chop through in 1 minute with nothing more than a "thunk". Alternatively, a good cordless drill can make short work of the lock face-plate with judicious use of a tungsten carbide bit... the only downside there is the ferocious self-feed once you break through to the brass. There's other methods, the hydraulic car jack etc. but all the quick methods require destruction of parts of the lock.
To discourage this, let's make the lock double-walled. The shackle is now steel-void-steel with the walls still being relatively robust >1mm thick to avoid accidents. Between the walls, we fill the void with a liquid. The liquid should be under significant pressure such that cutting through the outer layer causes a spray through the newly-made hole. The liquid should get all over the place, especially on the perp.
The choice of liquid is the fun part. Shops have been fitting clothes with dye-labeled tags for decades, but this isn't a huge deterrent to the average late-night scumbag so I propose the addition of a really nasty smelling substance, putrescine or thioacetone for example. Efforts should be made to make the liquid sticky and persistent so it hangs around on any tools/clothes for as long as possible.
If this proves effective then the hardened steel can be replaced by a tough aluminum since the cut resistance of steel is no longer required.-- bs0u0155, Oct 22 2018 Thioacetone http://blogs.scienc...rk_with_thioacetone [bs0u0155, Oct 22 2018] Bleeding_20Bicycle_...(Wasp_20Attracting) [xenzag, Oct 22 2018] Turns out it's baked : skunk lock https://www.bbc.co....s/business-546951881 bike so equipped stolen : "To avoid the lock, the criminals destroyed the entire bike rack instead." [Loris, Nov 10 2020, last modified Nov 11 2020] Most clever! The thioacetone is a nice touch. You might even use acid but a spill would etch the pavement and perhaps harm the bicycle.-- whatrock, Oct 22 2018 //spill would etch the pavement and perhaps harm the bicycle.//
Common bike materials are pretty acid-stable. Phosphoric acid is a good way of removing rust from steel for example. Aluminium is easily degraded by common strong acids AND alkalis in addition to being fatigue prone, so probably not a good idea to go with pH as your weapon. Incidentally, steel, titanium, aluminium and even bamboo frames are completely unaffected by HCN.-- bs0u0155, Oct 22 2018 See link.-- xenzag, Oct 22 2018 from the link
"..and destroying all residues by running them into the center of a wood fire in a brazier.”
Aha, this explains the spate of brassier-burning on campuses.-- not_morrison_rm, Oct 23 2018 [+] I've seen someone cut a U-lock, twice, in less than a minute. But he had the muscles for it, so I wouldn't call it easy.
My hunch is that, even now, thieves resort to less brute strength methods, such as picking or freezing, which would still go around your clever endeavor.-- 4and20, Oct 25 2018 I still think my original (of 2008) is a better deterrant than the copy which is a mere smell that's easily avoided with a mask. Try getting away from a swarm of wasps while covered in the substance they love most! (see link)-- xenzag, Nov 10 2020 Those chancers over at "Skunklock" have robbed my idea they have! I might chance an email to see what they've got to say for themselves regarding the originality of their creation....-- bs0u0155, Nov 10 2020 I posted my bleeding lock idea in 2008. Original is always best.-- xenzag, Nov 10 2020 Bugger, getting there first is actually the most offensive kind of theft. My only innovation then, is putting thioacetone inside, which frankly is a workplace accident lawsuit waiting to happen.-- bs0u0155, Nov 10 2020 For every lock, there's a workable flaw. But with any gaining of knowledge, let others* make the initial smelly mistakes.
* not that moral-- wjt, Nov 14 2020 random, halfbakery