The kind of lock you buy depends on where you park. If it's in a heavily trafficked area, you can probably get by with a good braided-steel-cable lock or U-lock for $18 to $30. But if you leave the bike overnight or off the beaten path, you'll need something more substantial. Kryptonite's Fahgettaboudit ($120) and Master Lock's Street Cuff SS ($125) are among the most theft-resistant. "You'd need serious power tools to get through either one of those," says Beth Annon, owner of B&L Bike Shop in Davis, Calif.
The Fahgettaboudit is a double deadbolt lock attached to a three-foot chain with 11-millimeter hexagonal links that can withstand 16 tons of force. It weighs just over 8 pounds, so you wouldn't want to take it on long rides. More likely, you would leave it hitched to the rack where you frequently park your bike. The Master Lock Street Cuff SS is 5.5 lbs. and looks like a police handcuff. It's intended for motorcycles but works as well for bikes. If thieves manage to foil either the Fahgettaboudit or Street Cuff, the manufacturers will replace your bike, up to a value of $3,500.SQUEALING
If you're worried about losing your saddle and wheels, Veratomic, Pitlock, and Kryptonite offer locking skewer sets that cost $35 to $50. These nifty devices work like regular skewers -- those metal pin-like fasteners that keep your seat and wheels attached to your frame -- except they have a little lock you turn with a key.
For added protection, consider one of the new bike alarms. The tiny battery-powered Cy-Curity alarm ($50; cy-curity.com) fits out of sight under your bike's seat and is triggered by a motion sensor. It comes with a remote control so you can make it start or stop howling at will.
Finally, for $10, you can register your bike with nationalbikeregistry.com, so the police can trace it to you if they recover it after it's stolen. You'll receive a tamper-proof I.D. sticker that shreds if thieves try to remove it. A shredded sticker is a red flag to potential buyers, making the bike at least as difficult for crooks to resell as one that is painted pink. By Kate Murphy