Countless accessories are manufactured for bicycles and bicycle riders. When thinking about such products we often think of helmets, lights, water bottles, specialized clothing, speedometers, and racks. One important accessory your bike should never be without is a good locking system. Just because you live in a relatively safe neighborhood doesn't mean you have no need for a lock.
Bicycle theft is a growing crime throughout the United States, and it doesn't matter where you live. Bicycles are relatively easy to steal and easy to sell or get rid of. They're an easy target for dedicated criminals, opportunists, and bored teenagers. Unless you never intend to leave your bike untended, you should invest in some sort of locking system. Even if you're just leaving it outside a convenience store for a couple minutes so you can go inside real quick, that's all the time a thief needs to make off with your ride. Don't think that thieves won't steal a cheap bike, either. They'll take whatever they can get their hands on, whether it's a rusted old girl's bike with faded streams dangling from the handlebar grips and a torn-up banana seat or a sleek high-dollar professional mountain bike with full front and rear suspension.
There are basically two options when it comes to locking systems for bikes. The most popular is the chain or cable lock with either a separate padlock or combination lock or with the lock integrated into the chain or cable. If this is the type of lock you're looking into, make sure that it's long enough to wrap around both wheels and the frame. With this style of locking system, the best choice is a chain that's as thick as you can comfortably carry.
If you'd prefer a cable lock, again, make sure you purchase the thickest one possible. The thicker the chain or cable, the more of a deterrent it'll be for thieves and scoundrels. The downside, of course, is weight. Cables tend to be lighter than chains, but they also tend to be easier to cut. You have to consider the importance of weight relative to your bicycling activity.
An avid racer is extremely concerned with weight, but such a competitor isn't going to be leaving his/her bike just lying around, either. In all likelihood, weight is not a serious issue to you. One advantage chain/cable locks have over other varieties of locks is their ability to encompass oddly shaped shaped objects such as trees, bushes, etc.
The other popular bicycle locking system is the U-lock. As the name implies, such locks have a big bend in them and are essentially big padlocks. Some are only big enough to go around the back wheel and the bike rack. Others are big enough to go around the frame as well. These sorts of locks are nice because they're quick to employ and come with clips to hook onto the bike frame without scratching it.
Whatever kind of bike riding you intend to do, unless it's solely competitive racing, you should invest in a good bike lock. You should get the heaviest one you can. An important feature to look for is some sort of guarantee by the manufacturer. Good locks come with assurances that if used correctly, and your bike is stolen, the manufacturer will reimburse you for the cost of your bike.