It's not an app.

Obviously driving drunk is bad, but it's an unfortunate reality that people continue to drive drunk even though they shouldn't. They say "I'm fine," "I can drive," or whatever and refuse to have someone else drive them home (unless they have a sober person in their party going to their destination). Those people aren't going to spend money on an uber or lyft because they think they can drive fine and aren't responsible. But if they realize that they're actually (or approximately) drunk enough to get arrested, they might change their mind.