Why a personal breathalyser could be the most important gadget in your glovebox over the festive season

Let's make one thing perfectly clear: if you've had a drink, don't drive. But I can't be the only one who’s had that niggling feeling, after a night out with some friends, that there's a chance your spot of indulgence might have left you over the limit by the morning.

If you're in any doubt, again, don't drive. But this is one of the many reasons a personal breathalyser might be a really good idea. It removes that doubt, and it could even save lives.

You can actually buy a single-use breathalyser for £2.99 these days, but AlcoSense, the market leader in this field, sells digital ones, and they're really clever bits of kit.

The best seller is the Excel Fuel Cell Breathalyser and it's the version I've been living with for a few weeks, to see why it sells so well and wins so many awards.

Primarily, it's a really neat device. Small enough to slip in a pocket or a bag, but loaded with the same technology the police use, and with a digital display to make your current state of inebriation extremely easy to understand.

You slide up a panel, attach a tube, blow into the tube until you feel a click, and then bask in the glorious confirmation that you haven't had a drink and you're perfectly safe to drive.

If you have been drinking, and for some reason you need confirmation that you're a danger to other road users, you will be given a reading in percentage of BAC (blood alcohol concentration) with a simple colour coding system letting you know if you're safe to drive or not.

Legal breath specimens are measured in micrograms of alcohol per 100 millilitres of breath. And the legal limit in the UK is 35 micrograms. It's stricter in Scotland, and there's talk of it becoming stricter in the UK. But as a rule, even one drink could put you over the limit.

The parameters the device works to are programmable, and you go through an initial setup to start off with. This is because limits vary by country, and the law might change one day. So it will always be able to tell you whether you're over the limit, whatever that limit might be.

The accuracy on the Excel is said to be within 0.15%, which is quite impressive. More expensive versions tighten this up even further, but the Excel is already £99.99. And it's advised that you calibrate it every 12 months at a cost of £24.99.

There are other clever touches, though. It has a built-in memory, capable of displaying your last 24 breath test results, and it even comes with batteries and a USB cable for software updates.

The little disposable tube you breathe into seems fiddly to slot into place, but it's effective, and you don't have to blow for very long. It gives you a reading very swiftly.

Overall, this is a device that shouldn't have to exist. Nobody should go near a set of keys if they have any doubts about their sobriety. But we're only human, and we often forget how much of an impairment even a small amount of alcohol can be.

In some countries, carrying a breathalyser is compulsory, and if the UK does lower the legal limit, devices like this will become very important. Because even a modest bender could have you over the limit by the morning.

We all have a responsibility to obey the drink-driving laws, but in exactly the same way a speedometer gives us a clear indication of our adherence to the rules of the road, there's no reason why a breathalyser shouldn't be part of our motoring toolbox too.