Company car drivers are being warned that they could be caught out if they trust cheap personal breathalysers currently on sale.
Some service stations are selling electronic breathalysers for as little as £4.99 to take advantage of the Christmas season, but experts are telling drivers not to rely on the equipment.
Many of the devices come with disclaimers warning that they should only be used as a guide, but the concern is drivers will miss the small print and use them as a definitive indication of whether they are fit to drive.
Roger Singer, of alcohol awareness experts Avoidd, said: “Cheap breath testers are of dubious accuracy and should not be relied on.
“It may say you are OK but the police officer’s device will be the one your future is decided on, not the garage’s.
“Even if it is accurate, your level could be rising as you absorb the alcohol, leaving you “over” by the time you drive.”
Simon Noble, a director at Risk Shifters, which supplies police-standard breathalysers, added: “I would not rely on a device costing £4.99 to provide me with accurate information about the level of alcohol in my system.”
The general view from experts is that cheap technology in this field may provide a reasonable indication of the presence of alcohol, but it is unlikely to provide you with reliable or consistent information.
“They also cannot hold their calibration for long, and because calibration is vital to assure the reliability of measurement, you can’t be confident of their consistency or reliability,” said Mr Noble.
Mr Singer said that apart from not drinking, the only reliable way to assess whether you are over the drink-drive limit is to add up the number of units, and count them down until you are alcohol free and therefore safe to drive.
It takes one hour to absorb one unit, and another hour (although this can vary by up to 20% either way depending on the individual) for each unit to exit the body.
A pint of Stella Artois, for example, which counts as three units, will take an hour to absorb and a further three hours to leave the system.