This post comes from Mark Vallet at partner site CarInsurance.com.

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Are you OK to drive, or should you call a cab?

Drunken driver © rolfo, Flickr, Getty Images
If you make the wrong decision, you may end up in jail or worse. You will meet lawyers. You will wear out your checkbook. And you will flinch when the car insurance bill comes.

Or you could buy your own personal alcohol breath tester and blow.

Devices cost $3 to $300, and their accuracy varies almost as much. The wrong device is worse than useless if it puts a drunk behind the wheel.

Yet more and more people are slipping one into their glove compartments. According to Wintergreen Research, sales of breath alcohol analyzers hit $284.6 million in 2011, and they forecast that number will climb to $3.2 billion by 2018 as prices fall and accuracy improves. In fact, French law already requires that all drivers carry one.

A guide, not a guarantee

In the end, the only number that counts is the one on the police officer's device.

A first-time DUI can cost thousands in court fees and will easily double your insurance rates, says Penny Gusner, a consumer analyst with CarInsurance.com. A second DUI may send your rates up 300% -- when you get your license back.

A final caveat: Blowing a number under the legal limit is not a free pass to drive. Impairment is more than just a number, and it is possible to be under the legal limit and still be arrested.

According to Gusner, the insurance premium jump for impaired driving is very similar to one for a DUI conviction.

"I would give myself a wide, wide margin of error," Gusner says.

A long way from the Drunkometer

While alcohol intoxication is defined as a blood alcohol concentration (BAC), testing blood is just not feasible when you are out on the town.

The modern, portable method of measuring breath alcohol concentration emerged in 1954, when Robert F. Borkenstein, a forensic scientist with the Indiana State Police, perfected the Drunkometer.

Breath analyzers work because alcohol shows up in exhalations. It is not digested, or even chemically changed in the bloodstream. While the police use desktop spectrophotometer units at the station to collect a reading that can be introduced in court, they use personal breath testers out on the road.

If you're shopping for personal use, four types are available:

  • Fuel cell. Allen D. Porter, the president of DrinkingAndDriving.o​rg, says fuel cell breath alcohol analyzers closely mirror what law enforcement officers use in the field. The fuel cell produces an electrical charge when it interacts with alcohol that can be precisely measured and translated into a BAC reading. Prices start around $100, and high-end models can run more than $300. 
  • Semiconductors. Breath testers that use a semiconductor as a sensor range from strictly novelty items to models that rival fuel cells in accuracy. The type of semiconductor material is what separates the toys from the real thing, Porter says. Silicon oxide-based models are more expensive, ranging from about $85 to $250, but are considered more accurate.
  • Crystals. These are single-use disposable units. You simply squeeze the unit to activate it and then blow into it. The crystals will change color if you are blowing over a set BAC level. According to Porter, they are popular with the military and are fairly accurate. These disposable units are priced about $3 but can be cheaper in bulk.
  • Key chains and phone apps. Breath testers that cost less than $50, come on a keychain or connect to your iPhone are best considered novelties for entertainment purposes. (Some apps, for example, track your eye movements.)

Personal breath testers are available at a variety of stores. Amazon carries a wide selection, as do Best Buy, Target and even Wal-Mart. Specialty websites such as Alcotester.com offer every brand under the sun.

Finding the right breath alcohol tester

Regardless of the type you choose, there are a few things you should look for in a personal breath alcohol analyzer:

  • FDA certification. The Food and Drug Administration considers breath testers to be medical devices and certifies them as safe after testing. Any device that lacks FDA certification is sure to be inaccurate.
  • A mouthpiece. Accurate analyzers have a mouthpiece that is attached directly to the device. This ensures that the sample is not contaminated by smoke or other pollutants in the air. The mouthpiece should be removable and washable. Most models come with extra mouthpieces.
  • Accuracy rating. An analysis is useful only if it is accurate. The highest accuracy ratings for testers run around +/-0.005. Most experts recommend a device with an accuracy rating of at least +/-.01.
  • Calibration. An accurate breath analyzer will require calibration at some point in its lifetime, with the exception of disposable units. If it doesn't require recalibration by its manufacturer, it may not be accurate enough to rely on. Fees range from $20 to $50. Currently there are models on the market that use a replaceable sensor module, eliminating the need for factory calibration.

Experts say you should wait at least 20 minutes from your last drink or cigarette to check your BAC. This will give the most accurate rating.

They also advise some practice -- in the security of your own home -- to make sure you know how to use the device before trusting it after drinking.

A possible consequence for poor accuracy? A highly accurate, state-sponsored model you'll have to use every time you turn the key.

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