You knew it was just a matter of time. So far, your smartphone has been able to do pretty much anything you ask of it — except tell you when you've had one too many to get behind the wheel. Thanks to the Breathometer ($20 and up), now you can. This keychain-friendly device plugs into the headphone port of your iPhone or Android device, and interacts with an app to give you an accurate measurement of your BAC. Shipments start this July.