For those who want to stay responsible, a keychain breathalyzer might not be the worst purchase in the world. We all know the typical time table of 1 alcoholic drink per hour, but there wasn’t a way to be certain until fairly recently, and some of these gadgets are pretty high-tech.

Number of keychain breathalyzer units to choose from

A keychain breathalyzer – or rather an electronic device that determines the blood-alcohol content (or BAC) by analyzing breath – has been around for some time. They’re pretty handy, as one of the units can (to some degree) tell a person if they’d be legally permitted to drive given their BAC.

That’s a good thing, since a DUI is fantastically expensive (a commonly-quoted figure is $10,000 all-in) and then there are the thousands of deaths per year due to alcohol-impaired driving.

Recent trends are to pair such with one’s cell phone via Bluetooth connectivity and a mobile app to go with it, such as the much-ballyhooed BACtrack Vio (according to CNET) or the Breathometer Breeze (according to AutoBlog), which show the data on your phone through the application.

The Breeze will also give a timeline as to when BAC will return to 0, dial a cab, ride-sharing service or emergency contact, and will even tell you about nearby hotels and restaurants. The Breeze goes for $100 and the Vio for about $40, albeit with less functionality.

Caveat Emptor

One might think “ooh, I’ll go out and get a keychain breathalyzer and be safe” right? Well, you may want to hold your horses. A test conducted by the Nampa, Idaho police department, according to KBOI2, a CBS affiliate in the Boise, Id area, found they weren’t perfectly accurate.

The Nampa PD took two people (one male, one female) and fed them measured drinks over a few hours in the police station, comparing readings over time using a BACtrack unit from Costco and their own Intoxilyzer unit. The fluids were measured to ensure both absorbed the same amount of alcohol, and were tested around the same time after finishing a drink.

Just after downing drink number two, the male subject blew a 0.2 BAC on the keychain unit and a .018 with the police unit; the female likewise registered 0.02 on the keychain but the police unit didn’t register any alcohol. Each consumed three more measured drinks. (Straight whiskey for the man and mimosas for the woman, in case you’re curious.)

At least fifteen minutes after the fifth drink, the male subject registers a .13 BAC on the keychain and a .075 on the police unit, the female gets a .12 and a .73, respectively. In other words, they tend to report different values than the police units, meaning they can’t entirely be relied on.

A cab ride can be cheaper

Similar tests of keychain breathalyzer units have been conducted by various other publications and websites, often finding smaller, less expensive portable breathalyzers fall short, but there are some that come close. Typically, those units are larger (often the size of a cell phone) and much more expensive.

Ultimately, just about everyone knows one drink per hour is the guideline. If you really need to test yourself to see if you’re OK to drive, you probably shouldn’t.