StemCAPtain - not a bike lock, but a bike CLOCK
Consider your bicycle's handlebar stem cap for a moment. It's right there in front of you as you ride, yet it tells you nothing. Colorado mountain bikers Graeson Lewis and Mike Hogan obviously thought that just wasn't good enough, and decided to put the humble stem cap to work. The result is their product, the StemCAPtain, which replaces a conventional cap with one that incorporates a waterproof analog clock, thermometer or compass.
First of all, yes, a cyclocomputer would give you all that information and more. Bicycle computers can be expensive, however, and even if they weren't, not everyone likes them. A wristwatch also does a pretty bang-up job of telling the time, although some people don't wear one, or would prefer not to while cycling – who likes a sweaty watch band, or an untanned area on their wrist in the shape of a watch?
To install the device, you just remove your old stem cap with an allen wrench, replace it with the aluminum base of the StemCAPtain, then push in the clock or other insert of your choice. A silicone gasket on the bottom of the insert should keep it snug and rattle-free. If your headset has already been properly set up, removing and replacing the cap shouldn't cause anything to go out of adjustment.
If you have any round pictures handy, you can also get a cap that simply acts as a picture frame. Lewis and Hogan are planning on future inserts that feature a bottle opener, altimeter, LED light, or a "digital multifunction device."
The StemCAPtain is available through the company website, and various retailers. Prices range from US$19.95 for a mini version of the clock, to $26.95 for a tilting version of the compass with a non-magnetic mounting bolt.