Originally Posted by Retro Grouch

How secure do you need to be?

The truth is that the first lock that you use with your bike, however cheezy, is about 90% effective because if forces the thief to bring a tool with him. Going from 90% effective to 99% effective is a progressively expensive, bulky and heavy process. There is no 100% effective lock. Anything made by one man can be cut by another given the time and technology.

Unless you have to leave your bike in a theft prone area I'd get myself a cable lock and wrap it around the seatpost. If you leave your bike in the same place regularly, leave a heavy secure lock at each destination to use when you get there.

Honestly, I seldom use a lock of any kind.