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The Kryptonite lock is an Ingersoll Rand-owned brand of bicycle lock for securing a bicycle to a pole or other fixture, when the owner wants to leave the bicycle in a public place. The basic design, made of hardened steel of circular cross section bent into a U-shape with a removable crossbar, has been emulated by numerous other manufacturers, and adapted with variations in size and shape for other applications, such as locking motorcycles.
The product was named after kryptonite, the fictitious substance that can thwart the powerful comic-book hero Superman. The name is used under a limited trademark agreement with DC Comics dating back to 1983.
The Kryptonite lock was developed in 1972. Before then, the only comparable security available was from a chain, which could weigh almost as much as the bicycle. (A common humorous observation in bicycle magazines at the time was that the total weight of a bicycle plus chain was constant regardless of cost, since owners of more expensive, lighter bicycles would buy heavier, more secure chains.) In the early 1970s the only proven method to secure one's bicycle was by the use of case hardened security chain with hexagonal links, but some cyclists were making the mistake of using inexpensive chains or cables that could be breached by thieves using commonly available tools. Indeed, local hardware stores would often sell inexpensive chain cut to length using simple bolt cutters. The first Kryptonite lock model was made of sheet metal cut and bent to shape, but the company soon went to the now universal circular cross section.
In an early test of the Kryptonite lock, a bicycle was locked to a signpost in Greenwich Village in New York City for thirty days. Thieves stripped the bicycle of every part that could be removed, but the lock resisted all attempts to break it. The innovative U-shaped design of the Kryptonite lock was subsequently adopted by several other manufacturers, with varying degrees of security. U-locks can often be seen holding naked rusty bicycle frames without pedals, gears, or wheels to bicycle racks.
A limitation of the Kryptonite lock is that it is heavy and bulky. Most (apart from the Fahgettaboudit Mini and M18 series) are provided with a plastic carrying bracket that will not fit all frames, nor will it retain the lock when riding over rough surfaces, making transport of this large lock difficult. For that reason many commuter cyclists leave this lock attached to a bicycle rack at their destination, rather than carry it back and forth every trip.
Until 2004, Kryptonite locks used the tubular pin tumbler locking mechanism. In 2005, after it was demonstrated that some tubular pin tumbler locks of the diameter used on Kryptonite locks could be easily opened with the shaft of an inexpensive Bic ballpoint pen of matching diameter,  Kryptonite changed their locks from the tubular to a flat key, preventing the use of cylindrically-shaped objects to defeat the locking system.[not in citation given]
- "Putting a Legal Lock on 'Kryptonite'". Law.com. Retrieved 2011-03-09.
- Stock, Ellen (23 Apr 1973). "Best Bits". New York Magazine. New York Media, LLC. Retrieved 6 January 2009.
- BikeBiz editorial staff (2004-09-16). "The pen is mightier than the u-lock | Bicycle Business". BikeBiz. Retrieved 2011-03-09.
- "The Kryptonite Lock-Picking Incident" Benjamin Running's original collection of lock picking videos and press coverage received
- Videos of Kryptonite locks picked by a Bic pen
- NPR interview with Benjamin Running, discoverer of the Bic pen lock exploit
- opening a $160 Kryptonite New York Chain - video from 2008
- "Debunking the myth of Kryptonite Locks and the Blogosphere" Dave Taylor, intuitive.com (retrieved 29 Oct 2006)