Disc brake lock
For extra security in a small package, check out the ABUS Detecto 7000 RS1 disc brake lock and alarm. Pushing the hardened steel locking mechanism closed against a brake disc — or any surface, actually — activates its 110db alarm, and any motion sets the alarm off, as we discovered in testing. 110db isn’t as loud as you might think, but it’s definitely loud enough to startle the average thief, making them think twice about trying to steal your bike. $139. MC