If you have ever wanted to try out a breathalyzer without being pulled over by the cops the Droidalyzer is the device for you. It connects to your Android phone using bluetooth and gives you an idea if you should be taking a cab even if you feel fine to drive. It also gives you some quick launch buttons based on the results such as call a cab or call a friend who is close. You can see the full technical details here including all of the details that you would need to make your very own (or a cool variation of the device).