I should say right at the outset that nobody is more opposed to drink driving than I. I don’t drink any alcohol at all when I’ll be driving, and my sole interest in a breathalyzer is to guard against those ‘morning after the night before’ moments when we may still have residual alcohol in our bloodstream. What I’m seeking is to be able to confirm that my reading is zero.

Look and feel

The BACtrack Vio measures 0.95×2.85×0.65 inches, so about the size of a typical car blipper. It does sit comfortably on a keyring.

It’s made of the ubiquitous ABS plastic, with a gloss finish. It doesn’t look or feel premium, but neither does it appear cheap and nasty.

The mouthpiece flips out from a recessed slot in the side, there’s a power button and a blue LED to indicate when it’s switched on. Finally, there’s a rear battery slot for a single AAA battery.

In use

The video above shows how it works, and it really couldn’t be any simpler to use. Open the app, pull out the breathing tube and hold the power button down for two seconds. Once the Vio connects to the app, you get a button to press to start the process.

The Vio takes a couple of seconds to warm up, then prompts you to take a deep breath before asking you to ‘Blow now’ and displaying segments to indicate how much more air is required for the analysis.

It’s worth following the advice, as a large breath is needed. This is because the unit uses the first part of your breath to ensure there’s no air left in the unit from earlier readings, before it begins its sampling.

The app then displays your reading, either instantly or within a second or two. Although the unit is analyzing your breath, it converts this reading into an estimated Blood Alcohol Content percentage, the standard measurement for intoxication used by law enforcement. Along with the percentage, it also provides a text description of what this means. Here’s a very low reading obtained about an hour after drinking a glass of wine:

The reading of 0.018 means that I have around 18mg of alcohol per 100ml of blood. Here, at just under half the UK drink-drive limit, the app warns of the likely effects.

I was pleased to see these warnings: studies show that driving ability is significantly impaired, with slower reactions and more risk-taking seen well below the legal limits of most countries.

Hitting OK displays a graph estimating how long it will be until you are sober. In this case, a friend and I started drinking at around 6.30pm, and entirely due to her bad influence, a second bottle of wine was opened at some stage in the evening. Here I’m well over the UK drink drive limit of 0.08, with a reading of 105mg per 100ml at 10pm.

The graph estimates that I won’t be sober until just before 5am – some seven hours later.


BACtrack makes a wide range of breathalyzers, some of them certified for law enforcement use. The Vio is the cheapest one in the company’s range, and is also its least accurate. The device is intended for the use I described earlier – to confirm a zero reading for ‘morning after’ scenarios, not to provide a precise reading of your intoxication level at anything higher than zero.

The reason for limited accuracy is the technology used in the Vio. Professional breathalyzers use fuel cell technology, and have built in pumps to ensure that all the air is removed from the unit before the breath-test begins. The Vio uses a cheaper semi-conductor based sensor, which is less accurate. This is the only way BACtrack could get the price down to $50.

To enable me to compare the accuracy of the two technologies, BACtrack also supplied me with their BACtrack Mobile unit, which has a fuel cell sensor. This is also a Bluetooth device that works with the app in exactly the same way, but is a bit larger and significantly more expensive at $130.

The above graph was actually based on my reading from the BACtrack Mobile. The Vio gave me a reading almost 50 percent higher (Vio reading left, Mobile reading right).

This underlines the dangers of attempting to use a consumer-level breathalyzer to try to determine when you are below the legal drink drive limit. While it over-estimated here, it could equally well under-estimate. The only safe use is to confirm a zero reading the next morning.

The safest approach would be to take a reading 15 minutes after you finish drinking (a delay needed to eliminate alcohol present in your mouth) and check the estimated time at which you’ll be sober, and then take a second reading in the morning before driving to ensure that it is zero.


It’s very rare that I drink enough to need to worry about the following morning, but I am a night owl with similar friends, so it is possible that we may be drinking into the early hours. While mostly this will be modest drinking, there are celebratory occasions where you have to wonder about the following morning.

I can recall one new year’s eve where we stopped drinking at 2am and I felt I had to wait until 4pm the following day to be one hundred percent confident that I was completely free from the effects of the night before (well, aside from the headache). It’s these situations where the BACtrack Vio – or Mobile, if you want to lay out the extra bucks on the improved accuracy – comes into its own.