Designed with extensive input from NYC bike messengers, the Kryptonite Messenger Mini U-Lock uses an 11-millimeter hardened steel shackle to fend off the efforts of determined thieves when you're running errands and stopping quickly for coffee in big cities. It's rated as a seven out of ten on Kryptonite's security scale, meaning it's ideal for quick stops in big cities and college campuses where cunning thieves are known for stealing anything not bolted down in mere minutes. With this security rating you can leave your bike out longer in rural and suburban settings without worrying about returning to nothing at the bike rack, fixture, or street pole. It's small enough to easily slip into your backpack or tuck into the back of your jeans when you're zipping around town delivering packages or simply commuting across town. Two stainless steel keys are included with a stretchy wristband for security. You can register your keys with the Key Safe Program by Kryptonite, which replaces lost keys for free without hassle. Other key features with this Messenger Mini U-Lock include a bent foot for easier release/entry, a rotating dust cover to keep the key hole clean, and wheel extender for locking up the rear wheel.