# Personal alcohol breath testers - accurate? **URL:** \ **Category:** Factual Questions\ **Created:** [February 15, 2004, 11:58am UTC](https://boards.straightdope.com/t/personal-alcohol-breath-testers-accurate/229339 "2004-02-15T11:58:38Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Maxxxie](https://avatars.discourse-cdn.com/v4/letter/m/f14d63/32.png) [@Maxxxie](https://boards.straightdope.com/u/Maxxxie)\ **Post date:** [February 15, 2004, 11:58am UTC](https://boards.straightdope.com/t/personal-alcohol-breath-testers-accurate/229339/1 "2004-02-15T11:58:38Z")
Hi all, There have been occasions where I’ve had a few drinks and later driven home, thinking I’m under the limit (I use the one drink an hour rule). But I’m always left wondering - am I _REALLY_ under the limit, or is it borderline, or what? Occasionally I see adverts for [personal breath testing devices](http://www1.jaycar.com.au/productView.asp?ID=QM7292&CATID=&keywords=breath&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=). Are these doodads accurate (yes, I know, standard disclaimers notwithstanding)? If I blow a 0.04 in one of these things, can I be reasonably certain I’m under the limit (0.05 here in QLD, Australia)? Max. ---
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [February 15, 2004, 4:55pm UTC](https://boards.straightdope.com/t/personal-alcohol-breath-testers-accurate/229339/2 "2004-02-15T16:55:14Z")
I have not tried that specific model but I have blown a .02 piss drunk on a hand held breathilizer. I figure that was at least .10 below what I should have been blowing. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 15, 2004, 5:29pm UTC](https://boards.straightdope.com/t/personal-alcohol-breath-testers-accurate/229339/3 "2004-02-15T17:29:32Z")
> [@Maxxxie](#): > > If I blow a 0.04 in one of these things, can I be reasonably certain I’m under the limit (0.05 here in QLD, Australia)? No, you can’t. In fact, the manuals that come with these things generally have some sort of disclaimer to this effect. Additionally, even if the reading _is_ accurate, other factors come into play, such as the speed of consumption and time. Even if you’re reading below the limit at the time you leave, you could very well be over by the time the police check you. The best rule, as always, is not to drive if you’ve been drinking at all. YMMV. ---
**Author:** ![seaworthy](https://avatars.discourse-cdn.com/v4/letter/s/a8b319/32.png) [@seaworthy](https://boards.straightdope.com/u/seaworthy)\ **Post date:** [February 15, 2004, 5:31pm UTC](https://boards.straightdope.com/t/personal-alcohol-breath-testers-accurate/229339/4 "2004-02-15T17:31:30Z")
I too blew like a .05 on one of those when I knew I was drunk. And if I knew I was drunk, that means I was well past the legal limit. But this was -the- cheapest one you could buy, so it’s possible that the better quality ones are more accurate. You could have a fun drunken experiment night with your friends. Do the calculations to find out how much alcohol the average person would have in the blood after consuming _x_ beers, rate how drunk you feel, then use one of those personal breathalyzers. A really good excuse to get drunk and learn at the same time. ---
**Author:** ![occ](https://avatars.discourse-cdn.com/v4/letter/o/8c91f0/32.png) [@occ](https://boards.straightdope.com/u/occ)\ **Post date:** [February 15, 2004, 9:01pm UTC](https://boards.straightdope.com/t/personal-alcohol-breath-testers-accurate/229339/5 "2004-02-15T21:01:44Z")
On a slightly different note, what about the breathalyzers that you see from time to time in bars? I’ve never seen these in the states, but when I was in Germany, you’d sometimes see coin-operated breath analyzers posted near the restrooms. Never tried one, but I’d suspect they’d be more accurate than the little handheld cheapie ones. And yeah, typical disclaimer. Breath analysis should only be performed by trained professionals. ---
**Author:** ![Maxxxie](https://avatars.discourse-cdn.com/v4/letter/m/f14d63/32.png) [@Maxxxie](https://boards.straightdope.com/u/Maxxxie)\ **Post date:** [February 16, 2004, 4:41am UTC](https://boards.straightdope.com/t/personal-alcohol-breath-testers-accurate/229339/6 "2004-02-16T04:41:37Z")
Thanks guys! That confirms what I had suspected. It’s all academic anyway, since I don’t drink anymore. I’ve seen those coin-operated ones as well. How do these things work, anyway? Max. ---
**Author:** ![erislover](https://avatars.discourse-cdn.com/v4/letter/e/71e660/32.png) [@erislover](https://boards.straightdope.com/u/erislover)\ **Post date:** [February 16, 2004, 5:22am UTC](https://boards.straightdope.com/t/personal-alcohol-breath-testers-accurate/229339/7 "2004-02-16T05:22:14Z")
> **[How Breathalyzers Work](https://electronics.howstuffworks.com/gadgets/automotive/breathalyzer.htm)** > > Drivers who can pass roadside sobriety tests -- by touching their noses or walking a straight line -- may still be over the legal limit for blood alcohol and be a hazard on the road. Breathalyzers help police find out who's really driving drunk.