With Kikkerland's “Bike Watcher” safety mirror , you can eliminate blind spots while biking without having to turn your body around to look. It's essentially a rear-view mirror you wear on your wrist — and a good sized one at that — allowing you to safely keep tabs on vehicles and other things to your side and behind you, resulting in less risk of you accidentally veering into the paths of those things.

Get it for $13 on Amazon.