> Are people convicted of DUI based on breathalyzer evidence alone?

Yes and no. In the US the DUI process looks like this (it's an interest of mine):

1) Pattern of impaired driving or other reason to justify the stop. This one is ridiculous and of course highly subjective - it includes things like a "sweeping turn" which is essentially not turning into the closest lane of traffic on a turn (think left turn and not turning into the left most lane), tires brushing a line, etc. Then obviously there's speeding, running stop signs, etc. In some states DUI checkpoints are legal where courts have ruled (essentially) that the Fourth Amendment doesn't apply for one reason or another to blanket stops for investigating impaired driving.

2) Some justification to start or continue a criminal investigation beyond the justification for the stop - this is the classic/infamous template: slurred speed, bloodshot/watery eyes, smell of alcohol, etc that you see in literally every single police report for impaired driving.

3) Field sobriety tests (FSTs). These are designed for you to fail and completely ridiculous. In the era of dash and body cams you're essentially going to put on a horrible performance that makes you look intoxicated or at least ridiculous even if you aren't. It's been demonstrated time and time again these tests are subjective and failure prone under ideal controlled conditions with known factors, let alone someone suddenly pulled out of their car on the side of a dark road somewhere...

4) Preliminary breath test (PBT). This is the small, roadside, handheld unit. You're usually going to get this no matter what. Obviously if this reports above the legal BAC limit you're going to get arrested. Depending on a variety of factors (how the officer feels, your FST performance, etc) you can be arrested for impaired driving regardless. This is obviously to account for other drugs that impair driving but of course do not register on an alcohol test. Additionally, you can be under the legal limit and still get arrested for impaired driving for the real/suspected "I had a beer but I also took a bunch of Xanax" type situations. To my knowledge these results are not admissible (or easily defeated) in court.

5) Certified test. When you get down to the police station (or wherever) they're going to have you do a breath test on a "certified" machine that's supposedly tested, calibrated, etc. Interestingly, in most places there are two tests, typically spaced by 20 minutes (or so). Apparently this is to account for the surface/residual alcohol issue. If you swish Listerine around your mouth and blow into a breathalyzer it will max out and tell you you're dead (essentially). Yet obviously none of this alcohol is in your blood. My understanding is for most cases the second reading is emphasized/reported/charged even though it's almost always lower because it eliminates a "residual alcohol" defense and the result is typically far over the legal limit anyway. This test is defined as "scientific" and admissible in court.

Of course in many cases where a breath test is refused or other drugs are suspected they can get a warrant for blood. Typically the barrier here is having a judge on call at 2 AM (or 10 AM, whenever) with a rubber stamp to issue these. That said, most places with DUI checkpoints now will have judges at the ready so more and more a refusal to do FSTs or a PBT at a checkpoint is signing yourself up for an almost instant blood draw.

But, to answer your question there have almost certainly been people convicted on breathalyzer evidence alone. However, "convicted" is a stretch here because to my knowledge there aren't a lot of jury trials for DUI - it's just not really worth it to anyone because the stakes for either side aren't really that high. Besides, in many states the Department of Motor Vehicles or whoever controls licensing has a completely separate administrative process that applies to your driving privilege.

I suspect in many cases where a breathalyzer has been the sole evidence even many (most?) innocent people will plead to "reckless driving" or whatever the prosecution offers - especially because in most places there isn't jail time for a first offense regardless, most states have some kind of hardship/occupational standard in place so that you can still drive for work, school, worship, child care, etc, and as mentioned the DMV process is somewhat separate anyway.

Because of the car-first culture in the US (vast distances, limited/non-existent public transportation, costs of ride sharing, etc) many people just drive with suspended licenses anyway which, to get back on track with tech here on HN, isn't what it used to be. ALPRs (automatic license plate readers) have really changed the game there.