KryptoniteKeeper 12 Standard Heavy Duty Bicycle U-Lock with Bracket (4-Inch x 8-Inch), Black

If you care enough to buy a lock for your bike in the first place, then you should care enough to get a lock that works better and easier than another lock, on top of giving you great security, so you will get into a habit of employing it all the time and not be lazy because the lock takes more effort to use. Lazy? Yes, and laziness is the biggest reason to not use a lock you bought to protect your bike. Just having a strong U-lock isn't good enough. You have to use it. An unused lock is the worst security feature a lock can have. Easier, with top security features is just better. You'll use this Kryptonite lock and that will save your bike more times than you will ever know. I put it in the same realm as building a better mouse trap.Having returned an On-Guard 5510 Mini U-Lock with Additional Security Cable (4 feet) to Wal-Mart where I had bought that lock, I chose this Kryptonite lock instead because, although On-Guard claims to be "obsessed" about security they sure aren't when it comes to product design. Bottom line is if you have a lock that is not as easy for you to use, then you will of course use it less and take a bigger risk with your bike becoming a crime statistic (stolen).Amazon had Wal-Mart beat on price for this Kryptonite lock, too. Comparing Amazon's service to Wal-Mart's wouldn't really help, since Wal-Mart forgot what service is years ago, and Amazon has consistently provided me with better service in all areas for many years now. Shipping for this lock, along with Avenir Tightrope Cables (12mm / 7 feet) - to make securing my bike a more complete security system for my wheels and saddle along with making more work for a would-be thief - and a Bell Dawn Patrol LED Headlight took just 4 days using Super Saver shipping, and you can't beat that. My Planet Bike Blinky "3" 3-Led Rear Bicycle Light, that I purchased at the same time, was packaged and sent along separately, but still arrived on the same day. Look for those reviews from me, too, should you like this one.This U-lock is very tough and I don't think you could easily find something that would cut through it, at least not something you could easily carry with you and go unnoticed. Seems more like someone would have to use a diamond wheeled grinder type of cutter with a power drill, at the very least, and that sure wouldn't be discrete or fail to draw attention. So while someone would not be able to easily steal your bike with this lock - if properly secured - for errands, short trips to a store, or in a busier type of place where you could even leave your bike all day, it won't be for you if you leave your bike in high-crime areas. I wouldn't trust this lock to be the only means of securing your bike at night for a long period of time or in an area with few people around and little activity during the day, as people being around and seeing your bike is one step in your security plan to make stealing your bike a less attractive option for a thief.One thing I really like about this Kryptonite lock over the On-Guard U-lock is that while On-Guard uses a dual, straight bayonet system on both sides of the locking arm to attach to the shackle, this Kryptonite U-Lock has an easier and better system to attach the locking arm onto the shackle. It's not dual, straight bayonet on both sides. One side of the locking arm of this Kryptonite lock has a short, angled part of the locking arm that helps you to guide and fit the locking arm into the shackle for that side, then you just swing the locking arm around the frame of your bike and a stationary object and clasp the other side of the locking arm (which has a straight bayonet fitting) into the other side of the shackle, then lock it by turning the key.To me, Kryptonite's is just a better design that makes attaching the locking arm to the shackle a little easier in warm, dry conditions and especially easier in cold, wet conditions. It also makes it easier to attach the locking arm to the shackle by obtaining a little leverage, if needed, for those times when you have to use a stationary object (like a pole) that is larger in diameter than some others when you lock up your bike. The dual, straight bayonet system for the locking arm with On-Guard's lock makes you press down and use compression alone (your muscle strength) for attaching the locking arm to the shackle. Kryptonite's design, with one side of the actual locking piece of the arm at an angle, lets you lock that side in and pull as well as push down on the locking arm if you need to.As luck would have it, since I have received this lock the weather has taken a turn from nice and warm to colder than a mother-in-law's kiss, with ongoing cold rain or drizzle and I have really found out just how much better Kryptonite's design and locking system works, which means it just makes it that much easier to lock up my bike. Locking up my bike properly is a habit I don't want to break. If a lock is more of a pain in the butt for me to use, like the dual, straight bayonet system On-Guard uses in their U-lock design, then I'm less likely to use it all the time, which means a thief will be more likely to take my bike. And that would make me sad.In short, you spent your good money on your bicycle purchase. Spend a little more and get a good U-lock like this one, or a stronger one if your area is more of a high-crime/high risk area, and use it along with a good cable like the Avenir Tightrope Cables (12mm / 7 feet). Little out-of-pocket cash, but you will have a security system that will intimidate most thieves, so the opportunists will give up without even trying and the more determined thief will move on to an easier target.For those interested in Kryptonite's Anti-Theft Protection offer, yes, you can register the lock and your bike with Kryptonite. You must verify your bike's serial number and purchase price with Kryptonite plus pay a yearly fee, along with other requirements and restrictions. It is all detailed in the enclosed package with the lock, and is available on Kryptonite's website if you want to know more.

Have had one of these locks for many years they work and protect your bike.

I've had this lock for almost a year now. First thing, all of the reviews complaining about the clamp being on the wrong side are just foolish. The clamp can easily be changed around via a simple bolt, and it can be made to fit any need. I've had the lock clamped to my bike the entire time and it works great and doesn't slide around or fall off.You'll also read a lot of reviews about this thing being broken. The thing is nowadays there are mini tools that can cut through just about anything, and quickly. I view this thing as more of a deterrent than a 100% full proof lock. Therefore I've used this lock combined with a thick chain lock to keep my bike secured in downtown Fort Lauderdale, and at the beach. It's always been kept outside. To put that in perspective, when I moved to the beach 4 out of 5 bikes were stolen from my building in less than 2 months... mine was the only one that wasn't. To be fair, I noticed most of the bikes had minimal security, such as small basic cable locks only, which were quickly cut (most of them were taken during the day!).Another thing is that where possible, you'll want to keep the keyhole pointed downward. I had his thing in the rain for so long with no issues, but one time the keyhole was pointed up and a heavy rain came through, and it was full of rust and pouring out just the same. Nevertheless, it's still held up and still does. But since the rain I've had the occasional complication with the lock mechanism. All in all, for the price, this is a great lock in my mind.

I guess they finally fixed the clamp problem, because I was able to use it the intended way. I only use the clamp when I don't have my backpack on me, so I can't speak for longevity. It does seem to be sturdy, though. The barrel turns freely when I operate the lock, given that you've inserted the key properly. No issues there. My model looks slightly different than the one pictured, and came with longer oval keys that have a solid feel to them. The lock itself is relatively heavy but that's to be expected. MUCH better than the Wally World locks. I feel confident leaving my bike alone with this lock, however, I do live in an area where bikes are not stolen that often, and I also never leave my bike for periods longer than 2-3 hours. You may want a stronger one if you live in a bigger city or leave your bike outside. ALWAYS ALWAYS ALWAYS pair a U-lock with a chain or wire lock with a separate padlock when leaving your bike for extended periods of time. I cannot begin to describe the way people at my university lock their bikes up. Despite having decent locks, they somehow manage to make it scream "PLEASE STEAL ME". Please don't be careless; you're the only one that will get burned from it. This lock is definitely worth the price. Very satisfied!

EDIT: Two days after I wrote the 2 star review below, my bike was ALMOST stolen. The lock showed evidence of being cut with a saw in three separate locations but the perpetrator obviously gave up before getting all the way through. Despite any inconvenience with the lock sticking, I'm very grateful I had this lock on my bike. I just ordered the same lock again as a replacement.Original review:After about of month of multi-daily use, the locking mechanism gets stuck about 50% of the time. It opens after jiggling the key a few times, but is inconsistent.