Well I'm the "Idiot" who is trying to start a breathalyzer franchise to deter unsuspecting people who think "Well I just had a few drinks" from getting behind the wheel. As a previous bouncer at a bar, I've seen plenty of cases where people think that their "couple of beers" have not put them over the limit and drive anyways.
I've seen people do this before ... if some guy blows a .05 in the machine and decides that means their fine to drive, he can always try to claim that you said he was okay to drive or some such thing. He might be able to make a successful claim for damages against you. Why risk it? Even if you win you might have to spend money to defend yourself.
I just want to cash in on it and provide a service that isn't there at bars. My rational thought is if someone who gets a test prior to driving may make the better judgement to not drive if over the legal limit.
what do you think
I think you underestimate the lack of judgement that comes with alcohol consumption.
Far too many people seem to think that if they are UNDER .08 they are good to go! That's simply not true! What you might be doing is giving people the green light to drive. If people take the test and blow .08 or better, will they actually not drive and call a cab? Maybe. My gut and world experience tells me no, but I suppose it's possible.
However, you do potentially open yourself up to liability if you do this. I have seen bars that offer this as a service and even have machines AT the bars that you can pop money into and blow. But, I believe they have disclaimers all over them such as that the device is for entertainment purposes only.
If you are truly doing this to provide a service, great ... but, since you are accepting money it is arguably a commercial venture and that could land you into a whole different ballpark in a couple of areas.
If you google the relevant terms you will find arguments both for and against them. If it were me, I wouldn't do it.