Sure, the Jaws of Life is great at cutting a car in half, but the Jaws would never fit on a keychain, and if it did, it wouldn't be to convenient to carry around. The BodyGard (yes, the manufacturer purposely spelled it wrong) is a 5-in-1 emergency tool that can fit on a keychain and provide a ton of help in a bind.
This device has a spring-loaded automatic glass breaker, seat-belt cutter, sonic alarm, red distress signal and a bright LED flashlight. It also includes a quick release for the keychain attachment to get it off if the keys are still in the ignition. It is also very usable as a attacker deterrent and could be tons of fun with a hyperactive pet (minus the glass breaker, or belt cutter, of course). And it's all available for $15. [Thinkgeek]