A Google+ friend asked me today whether handheld personal breathalyzers were accurate. Interestingly, I saw one today at Costco. Some of these devices are stand-alone and some are attachments to common smartphones like the iPhone and Android devices.
I appreciated the question, but it is the wrong question. Reliance on a personal breath-testing devices or a Breathalyzer at a bar can potentially lead to a DUI arrest.
You have to understand how alcohol is metabolized and absorbed by your body to understand the concern. When you are drinking your body starts to absorb the impairing affects of the alcohol while, at the same time, it starts to metabolize the alcohol. As a result, if you only consume a small amount of alcoholic beverage over a long period, your B.A.C. may not even rise to any significance.
However, that is not ordinarily what happens when people drink. Most people consume enough alcohol to allow an increase in their blood alcohol level above and beyond their body's ability to metabolize. As a result, their B.A.C. starts to rise.
This is where a personal breathalyzer can create a false sense of security. Your B.A.C., when tested, is a number at a point in time. However, if you have recently consumed alcohol, you cannot know if your B.A.C. is still rising, whether it has leveled off, or it is declining.
Chances are that your blood alcohol will be rising if you recently consumed alcoholic beverage. As a result, if you are tested by the police (during a DUI arrest or at a check point) your B.A.C. will likely be higher, later in time. People always assume that their level will decrease as time passes, however, that is scientifically incorrect. Eventually it will decrease, after first rising (even after drinking has stopped).
For this reason, use of personal breathalyzers can increase your chances of getting a DUI. My advice is to drink responsibility and have a designated driver. Remember, a designated driver is not a person who has had the least amount to drink. It is the friend who has had nothing to drink. Be safe and drive carefully!