The iBreath is a device which connects to your iPod. The device has a tube sticking out of the side so you can blow down it to measure your alchohol content level. This is accurate to 0.01 BAC. To add a twist to this, the device doubles up as an FM transmitter. It makes you wonder if the device will not work when your level is too high 
The iBreath costs $50 although I think 1 drink is too many to drive! So be careful out there.