Random Breath Testing: Did My Cop Stuff up?

So I was at a wedding on Saturday and from 5pm to 10pm, I had six beers (Lashes, yum) and one shot.
Being an engineer, I entered it into an app to calculate my BAC, which said around 0.04 when I left, quite close to the limit, but not over.
Then after about 10 minutes, as luck would have it, I got stopped for a random breath test. The cop does the usual, asks for my licence, asks if I've had anything to drink, to which I respond "yes".
He then wants to do a breath test, but then decides to do the counting test first, even though we both assume it's a foregone conclusion.
I count, he looks at his machine and then says "You're free to go", I reply "Really?", he just says "Yes".

So did the cop stuff up, was his machine faulty or am I a strange human specimen?


  • If you said you drank recently they have to wait. He couldn't be bothered if you seemed sober.

  • +254 votes

    I'm pretty amazed somebody would rely on some app to determine whether to drive or not, and then when it spits out 0.04 still choose to drive. The mind boggles.

    • Science FTW!

      • How does the app factor in your BMI, liver function, genetics etc? Must have some advanced functionality!

        • It takes height, weight (BMI), gender and age, from memory.
          If anything, I slightly underestimated my weight and over estimated the alcohol in the beers (Lashes are only 4.2% and 345ml). So I have a safety factor of 20%, which to me, seems reasonable. Plus, I could have gotten an extra 15 minutes+ for my second test, had I blown over.

          On a side note: I rarely do this, usually my wife drives, but it was the odd occasion where she felt like a drink so I said I'd drive. I've also not lost a single demerit point, nor have gotten even a parking find in the past decade, so I'm fairly safe in general.

        • Well he did say he was an engineer, not a medical scientist!

      • Engineering and science disavow any association with BAC estimation. :p There will be a disclaimer. Does it use the accelerometer?

        • I obviously know it's not perfect, but it does give you a figure that should be in the right ballpark.

          • @spludgey: yes and a ballpark of 0.04 would be safe to assume you are OVER. the margin of error is too great to assume that is safe.

      • +16 votes

        Judge: your guilty
        OP: but your honour .. the app said I could drive

        • Judge: You're guilty.
          OP: For what?
          Judge: For blowing under 0.05.. oh wait, you're not supposed to even be here.

      • I don’t care what you think is science and numbers and all that 💩 if your relying on an app to tell you if your alright to drive then you are a irresponsible and dangerous individual who should have his license taken away from him. So many people drink and drive these days and cause so much havoc and you come on here boasting how you use an app and got away with it. Shame on you. Wake up to yourself. Next time you might kill someone.
        Drink and drive. Your a bloody idiot.

        • Imagine if every driver is reasonable like the OP who leaves plenty of buffer for his calculated risk taking.

          The road will be a much safer place. I don't mean it in any sarcastic way.

        • I can’t help noticing the irony in calling someone “a bloody idiot” and yet can’t spell “you’re” 😂

    • This is why the OP would be a great engineer. It’s all about risk and and efficiency (laziness).

      During my uni years I would do this all the time. It was harder as I was on my Ps when it 0.02. I drunk 8 bottles of Hahn light during a 4 hour period. I stopped drinking 1 hour ago, am I okay to ride my motorbike. Probably should wait another 3 hours.

      The same with exams. If I walk out of the exam now will I pass? I have answered 75% of the exam and would have about ⅔ correctly answered so probably a pass but with margin or error a pass conceded at worst. So this assignment is only worth 6% of my total but the effort seems require work that would be for a task worth 20%.

      • Haha that wouldn't work with optometry. Oh you got 49.5% on the exam? Congrats, you just failed the whole unit, see you again next year. And no units for you next semester- everything is a prereq.

      • Playing fast and loose with human life does not a great engineer make. I guess he'd fit right in at Boeing.

    • -1 vote

      Interesting point.
      I would probably error on the side of caution of being closer to 0.01-0.02 (the equivalent of 1 drink) before I drive.

      Alcohol absorption (how much your BAC increases after 1 drink) and metabolism (how quickly your body gets rid of alcohol and how quickly your BAC drops) vary quite a bit from person to person.

      What we need is standard deviations or confidence intervals with these estimates. so we say there is a 95% chance your BAC is between 0.0-0.5.
      I'm sure it would be there in the original studies which worked out formulas for prediction. (Add to my list of things to do).

      On unrelated noted your avatar is broken. (It's blue…)

    • The app doesn't mean shot.

      It's just an excuse people will try to use when they get done drink driving.

      " But the thing said I was ok sure ?!?! "

  • +58 votes

    You're a crap engineer and a worse person, you put yourself and others at risk driving drunk.

    • I've reported him to the FBI.

    • Do you only drive completely sober?
      The app is far from perfect, I'm not disputing that, but it's certainly better than estimating without one.

      • Do you only drive completely sober?

        I do

      • +15 votes

        I do as well.

      • Does the idea of only driving completely sober seem strange to you?

        • No, 99.99% of the time when I drive I'm completely sober.

          • @spludgey: I understand calculated risks are what engineers do all the time, and what you did was perfectly reasonable.

            It's just humans are emotional creatures. Reason is a luxury. So be prepared for all the condemnation!

            I'd rather someone like you taking a calculated risk, than some negligent driver making mistakes without realising them. If only every drink driver is like you. The road will be a lot safer.

            • @Bad Company: I think the issue here is that it's not just his calculated risk, it's a calculated risk for the other people using the road at the same time (which they didn't agree to take).

              The guy had an RBT and passed, so I don't think there's a problem here. But, if an app says you're close to the limit (the limit being an arbitrary line, over which you're assumed to be a danger to yourself and others) and your response isn't "let's sit down for an hour and drink some waters", it's "chuck us the keys", then there's a bit of arsehole to your attitude.

              • @mattsamp: At that level it's more a calculated legal risk than a calculated public risk. In California the limit is .08 thus even .06 would be considered 'safe'.

              • @mattsamp: Actually the public around him did agree to take said risk, since the legal limit is below 0.050, anything up to that point is deemed acceptable. Every driver on the public road have to agree to the road rules prior to holding a licence, therefore by extension they agreed to put up with drivers with a BAC of less than 0.050.

                Since OP said he left plenty of margins of error, he was just taking a legal risk that may see him blow a little over 0.049, rather than public safety risk where he drives drunk.

                Like I said before, I wish every drink driver is like the OP.

          • @spludgey:

            No, 99.99% of the time when I drive I'm completely sober.

            I find that that to believe for anyone that's a regular drinker. 99.99% = 3.65 days/year you're driving after a drink, just seems very low. You might be diligent about taking public transport/taxi after having a drink, but you have to remember you might still have a detectable amount of alcohol in your blood the following morning.

            Something like 95% might be more believable.

      • I only drive when completely sober, OK in my young 20's I did drive probably over the limit a couple of times but I'm not proud of it and I certainly didn't feel the need to boast about it on an internet forum.

        • Evidently, I didn't drive over the limit.
          Nor did I think I was boasting, more perplex of why I didn't get a proper breath test.

    • Actually he would be a great engineer. A great combination of risk calculation and efficiency (laziness)

      • Yeah - OP's an engineer, not a physicist. It's all about practical application. And practically, he was under the limit and evidently able to drive. Seems like that'd pass muster in any other context - not perfect, but within tolerances and able to perform the required function.

    • He wasn't drunk in the eyes of the law. if he'd blown over the police would have had him on toast.

      Have you ever been at a measured 0.049? I have and you would not think from both the personal perception and external observation that a drink had been taken. This is why f-wits that do feel drunk should have the book thrown at them.

      • He wasn't drunk in the eyes of the law. if he'd blown over the police would have had him on toast.

        How do you know?
        They never did a breath test only a screening test

        • A screening test which he would have failed if he was drunk.

        • It's a go/nogo test. If he was over 0.049 he would have given a "fail" reading which then would have required an evidentiary test.

          Even if he passed the first test, if the officer suspected the driver was under the influence of alcohol he can do a 2nd test.

          • @brad1-8tsi:

            It's a go/nogo test.

            That's correct

            If he was over 0.049 he would have given a "fail" reading.

            That's incorrect.
            The count to ten test is an indication test only. It detects any alcohol.

            If it gives a positive result you blow into the straw.
            If that detects over 0.049 then you do an evidentiary breath test.

    • He was under the limit and driving within the legal parameters. Get off your high horse mate.

    • Except he wasn't, so maybe you're a crap person

  • +37 votes

    As someone who has experienced a friend lose a limb and their career due to a drunk driver, I think you're crazy to go to a wedding and take your car.

    Buy an actual breathalyser if you ABSOLUTELY NEED to drink then drive. Or just taxi/uber like the rest of us.

    • I wasn't sober, but I wasn't drunk either.
      A breathalyser isn't necessary better, as the BAC can rise a while after drinking, as someone mentioned.

      Let me reiterate: I'm 98% sure that I did not break any law and was never over while driving. But I concede that whether I was over or not, my reaction times would have been impaired (within allowable limits).

    • I only ever drive 0.00, but once when out we all paid for the breathalyser at a club and I blew well under others and under 0.05 when I could barely walk. Personally I would never drive even at 0.025. I think BAC mileage varies.

      • Those machines in the clubs are junk to generate profit. Probably never been serviced or calibrated. I wouldn't trust them anymore than the condom vending machine next to it with unknown years old rubbers in it.

        Actual handheld devices with a fuel cell sensor are fairly accurate.

        • I used to sell 99$ breathalyzers, then discovered they had to be calibrated every 12 months, and cost $75 + postage each way.

    • He was not drunk.

  • A good engineer would have taken into account other factors and probably be dissatisfied with the open ended answer and bought a breath tester instead.

  • +4 votes

    Cop dodged a bullet here

  • With your engineering degree, why not taking to high court? instead of Ozb?

  • Top