I came up with this cool idea for a new bicycle lock. I call it a drivetrain lock (or drive lock for short).

Basically you take a very small padlock and attach it to your bike's chain. This prevents the crankset from fully rotating, which means the bike can't be ridden away. This pretty much eliminates the use of the bike as a getaway vehicle.

Lots of useful situations:
1. It works great for messenger use or errands. For all those times when you have to leave your bike within site but unlocked.
2. It's also really useful if you put your bike on the front rack of a city bus. Use a drive lock first, and it will stop the "grab and ride" thefts of opportunity.
3. It also makes a pretty good supplementary deterrent for short-term use. Like if you only have a cable lock and need to stop in a store for a few minutes.
4. Or for locking up while you are at work or school. In downtown or high-crime areas, a drive lock provides one more barrier of resistance (in addition to a U-lock and cables).

The lock I use is made by Masterlock (model 121T). Most chain drugstores like Walgreen's sell them for $6. You can keep it on your keychain since it attaches as one piece.

Hope everyone likes the idea. I always get a lot of interesting comments from people when I use it. Most have never seen anything like it before.