Bike commuting means bike theft. You need a good lock. We used a hammer, bolt cutters, and a Dremel rotary saw on these (way beyond what most thieves would deploy) to see how they'd hold up.

1. Kryptonite New York Legend 1590

The 15-mm-thick hardened-steel links on this 10-pound beast slide uncooperatively when you try to violate them. Bust the plastic off the dead bolt and it reveals a scarier-looking steel shackle. The Dremel took a battery-killing 15 minutes to get through one link, and we still needed a second cut to slide the neighboring link out. Your bike is safe.

2. Blackburn San Quentin

Like any U-lock, this presented a tantalizingly long expanse to work with, but the hexagonal profile of the 18-mm-thick alloy steel makes it hard to find a good angle. The saw got through in about eight minutes, but we'd have needed a second cut to remove the thing: It locks on both sides. And by that point we didn't have the juice to go full-power for another eight minutes.

3. Trek U-Lock LS

Our bolt cutters and hammer got nowhere against Trek's 13-mm hardened-steel shackle. But the big 11.5-inch-long U, which makes for hassle-free hitching, offers plenty of room for sawing. In four and a half minutes, we were clean through with the Dremel and sliding off the opposing piece; unlike the Blackburn, this locks on only one side.

WIRED Light and intuitive. Spare design makes it the best-looking of the group.

TIRED Antitheft protection runs to only $1,500.

$60, trekbikes.com

Rating: 5 out of 10____4. Kryptonite HardWire 1518

Cables are deterrents, not defenders. Even Kryptonite gives the HardWire a 5 on its 12-point security scale. The lock can withstand a hammer attack, but so what: A pair of 24-inch bolt cutters (far from the biggest available) got through the 15-mm braided-steel key cable in two minutes. The Dremel took 30 seconds.

WIRED Light, flexible, and portable. Six-foot length reaches both wheels.

TIRED For friendly areas only. It's about as daunting as a licorice whip.

$53, kryptonitelock.com

Rating: 4 out of 10____5. OnGuard 5023L Rottweiler

While OnGuard makes some of the best chain locks, this armored cable is more practical in terms of weight, even at 7 feet long. It's a 30-mm twisted-steel cable inside a length of steel vertebrae wrapped in a vinyl cover. But cut through the coating and you see the Achilles' heel: gaps in the vertebrae that expose the cable. The Dremel took it out in less than three minutes.

WIRED Built-in light on one of the keys. Recessed ball lock resists crowbar attacks.

TIRED Price. Theft.

$135, onguardlock.com

Rating: 4 out of 10____6. Master Lock Street Cuff 8200D

The clever pivot point in the middle makes it hard to get any leverage with a tool. Unfortunately, the steel closures (which are small enough to limit your anchoring options) aren't very thick. They resisted our saw for all of two minutes. Worse, it took only a couple of hard whacks with the hammer to bust open the locking mechanisms.

WIRED Light and compact. $3,500 antitheft guarantee. Might actually work as handcuffs.

TIRED Looks tougher than it is.

$62, masterlock.com

Rating: 3 out of 10