To get drinkers to play it safe after a night out, three young entrepreneurs are banking on a police-grade breathalyzer that they call Alcohoot. The $99 device plugs into an iPhone and communicates with an app. After a gusty blow it logs and displays your blood alcohol content to within a hundredth of a percent. If you're above the legal limit, it helps you search for the nearest greasy spoon -- or a cab.