This is the ultimate gadget to save you from making a big, big mistake—driving after having had too much to drink.

As most people know, alcohol affects people in different ways; the effects of three beers on one person can be vastly different in another. Simply put, there’s no easy way to define how much is too much.

Hence, the personal breathalyzer; an objective method of measuring your blood alcohol content. Keep it handy in your car and use it after drinking to find out if you’re safe to drive.

There are a number of these on the market, and while I can’t say which one is best, you can expect to pay in the range of $50-150 for one.

One that seems to get good ratings and is recommended by Lew Bryson is the AlcoMate—pick one up here or here.

And—be sure to use it.