> Driving under the influence should be detected by professional law enforcement observation.

It is. I've been pulled over a few times in my life. Never had a breathalyzer test done, because they assumed (correctly) that I hadn't been drinking. But human observation is far from perfect. And even harder to defend in court.

> Then if suspected after being pulled over, tested clinically. This is not that difficult.

What does "tested clinically" mean. If you mean a breathalyzer for cannabis, well then that's what this is. If you mean a blood test, well, it's pretty hard to get someone to a lab in time to detect meaningful levels of THC from recent smoking, as the poster of the Launch HN notes. It is pretty difficult.

> Even if a certain level of any substance is detected and measured, level of impairment is not.

This is tricky. As with alcohol, different people have different tolerances. Some people can have one drink and feel tipsy, others don't feel it at all. So we set a legal limit for how much alcohol you can have in your blood, regardless of how you feel. You have to draw the line somewhere and we've decided as a society to set it at a point that's more conservative in order to reduce accidents related to drunk driving. And there are plenty of drunk driving accidents. This would do the same thing with pot. Yes, you might feel perfectly fine, but I don't want your subjective opinion of how well you think you can drive under the influence of marijuana to be the determining factor in whether we let you drive after smoking pot or not. If you want to smoke, stay put or take an uber.

>Yes, you might feel perfectly fine, but I don't want your subjective opinion of how well you think you can drive under the influence of marijuana to be the determining factor in whether we let you drive after smoking pot or not.

Couldn't you approach the same problem by testing the capabilities of the driver rather than testing the amount of a substance in their system (after all there are countless substances than can impair a driver, not just alcohol and marijuana)? Would an improved field sobriety test be a more appropriate product than an improved breathalyzer?

> Would an improved field sobriety test be a more appropriate product than an improved breathalyzer?

Yes, do you have such a test?

No, but I'm also not the one selling breathalyzers either. I was merely offering a hypothetical product that people could work on that would both meet the need this company identified and satisfy most of the complaints from the community here.

I'm not sure what this hypothetical product would measure. Driving ability? If so, what if it was found that that would discriminate against classes of people? How do you gauge driving ability anyway? I would probably win a formula one race against my wife, but she's much better at paying attention to the road on long, boring stretches of highway. But I can't imagine that it's easy to test for that.

Meanwhile, this product tests for something that's easy and simple. Have you recently used marijuana? It gives a yes or no (and presumably a level of some sort). It's not the perfect test, but it seems like a fallacy to argue against this test on the basis of a better test that doesn't currently exist.

You don't have measure actual driving ability. Current field sobriety tests don't do that. You can instead test coordination, balance, cognition, reaction time, etc. These are the things we actually care about when we talk about impaired driving. So why don't we test them instead of testing for one or two specific substances?

This is incredibly ticky-tacky and can lead to bad outcomes based on race, mental abilities, etc.