It's not only Olympic superstars who misjudge their alcohol consumption.

Earlier this week, Michael Phelps was arrested in Baltimore for driving with a blood alcohol reading of 0.14. He's apologized for his behavior, but the goal is to prevent folks who are over the limit from getting behind the wheel in the first place. Not surprisingly, there are gadgets – and apps – to help stop them.

You may have faced a situation in which you were trying to convince a friend not to drive, or you may have wondered if that last glass of wine was enough to impair your own judgment. A personal breathalyzer, which cost from $30 to $120, can do the trick by demonstrating objectively that you or a companion has had one – or more – too many.

Matchbox-sized personal breathalyzers measure blood alcohol concentration (BAC) based on the level of alcohol in your breath (about 10 percent of the alcohol you drink is released into your breath). From that reading, they estimate the percentage of alcohol in your blood. Generally, these devices use either a semiconductor sensor, which is small and inexpensive, or a fuel cell sensor, which can be more accurate and is used by law enforcement in portable devices. I tested two models that work with smartphones.

The Breathometer costs $50 and plugs into the headphone jack of an iPhone or Android smartphone. It uses a semiconductor sensor and an AAA battery that should last for up to 75 tests. The company recommends waiting until 20 minutes after your last drink for a more accurate test, as it will avoid higher results from the alcohol residue in your mouth. It takes about a minute to warm up the device, and then you’re prompted to blow for four to five seconds through a hole from about two inches away.

I had to retest for accuracy several times. And in one case, after I toted it around in my briefcase, the sensor collected too much lint to be effective. (It was easily blown clear, however.)

But the Breathometer was reasonably accurate. If anything, it tended to err on the side of caution by yielding slightly higher results. One evening, after a glass of wine, I blew a 0.03, eliciting a yellow warning and a note: "You should be sober at 12:17 AM" – roughly 2 hours away. A retest brought the number down. And here’s a bonus feature: The app provides a list of local cab companies.

Breathalyzers need to be calibrated regularly, and the Breathometer is no exception. The company says it should be recalibrated every 250 tests, or after nine months. The mail-in service costs $20

Alcohoot, another smartphone accessory, is a competitor. It costs $100, but it uses a fuel cell sensor, the same technology police officers use, and it has a rechargeable lithium-ion battery that will last for up to 500 tests. It's slightly larger than the Breathometer, and it works almost identically. You blow through a hole where the sensor is. The company recommends using one of the eight washable and reusable plastic mouthpieces that come with the device.

The Alcohoot started up more quickly and delivered consistent results, probably because I used the nozzle. I blew a typical 0.017 after a large glass of wine. The program reminded me that the legal limit is 0.08 BAC. The app charted my reading and the time of day, and it recorded that I was below the red line that denotes the legal limit. It also warned me, "You may begin to feel moderate effects." I noted that I could call an Uber, Lyft or Hailo car service from the app.

In addition to being more accurate, the higher-priced Alcohoot doesn't need to be recalibrated as often as the Breathometer. The company says it lasts for up to 1,000 tests or one year. Its recalibration service costs $30.

I trusted the Alcohoot more than the Breathometer, mainly because of its ergonomics, but keep in mind that while these are FDA registered devices, they are not a license to drink and drive. Both companies repeatedly note that you should not do so.

Furthermore, breathalyzers can be imprecise. Using a mouthwash or breath spray can affect the accuracy of the measurement, and alcohol affects everyone differently. On the other hand, having one of these devices at the ready to convince a friend that he should take a cab or sleep on the couch could end up saving a life.

 

John R. Quain is a personal tech columnist for FoxNews.com. Follow him on Twitter @jqontech or find more tech coverage at J-Q.com.