The guy in this video has the best job ever. Tokyoflash Japan, a high-tech watch company, gave him a whole bunch of money to spend on booze so he could try out a new breathalyzer watch.
The watch, called the Kisai Intoxicated, has a built-in breathalyzer and sobriety test. If you blow into the sensor, the watch will change colors to show how drunk you are. Green means you're sober, yellow means you're "buzzing" and red means you're totally drunk. You can also test your reaction time (often the first thing to go after a few drinks) with a fun game.
Remember, though, as the company's website states, this watch is just for fun. It's more of a party trick than a scientific test, so don't rely on it if you actually need to know if you can operate a vehicle.