Breathalyser Readings And Terminology

Breathalyser Readings 

Breathalyser Terminology


  • BAC= Blood alcohol concentration
  • Commonly displayed as a percentage %BAC or mg/100ml. 
  • Few breathalyzers on sale in UK display in BAC 


  • BRAC= Breath alcohol concentration.
  • Most newer models of breathalyzer display BRAC in mg/L (milligram per Litre)

Breathalyser Accuracy

  • Breathalyser accuracy= the selectivity achievable when the breathalyser sensor is correctly calibrated.
  • This is often displayed as the variation accepted in %BAC ie +/- 0.01%BAC means the breathalyzer will display with an accuracy of + or - 0.01 on the display 0.05 the breathalyser may display a variance of 0.04 to 0.06 on a series of 3 tests done in succession.
  • A greater variance would indicate a possible loss of calibration, sensor failure, evaporating mouth alcohol or poor breath sampling technique.

Breathalyser Calibration

  • Breathalyser calibration = the service which sets the reading accuracy of the sensor.
  • Breathalysers which do not have interchangeable sensor modules will need to be sent for service periodically for a calibration service to maintain their accuracy.

Chemical Breathalyser

  • A chemical breathalyser is a single-use disposable breathalyser kit which you blow through.
  • A chemical reaction takes place between the alcohol in your breath and the crystals in the breathalyser and produces a colour change.
  • The colour corresponds to a particular level of alcohol in the blood. They come with a chart so that you can interpret the results.
  • They are highly accurate around 98%, and are a very good first line alcohol screening tool.
  • They have an expiry date after which they should be discarded.
  • Browse our range of single use chemical alcohol breathalysers

Digital Breathalyser

  • A digital breathalyser is an electronic breathalyser rather than a chemical breathalyser.
  • It contains a sensor that detects alcohol in the breath sample.
  • The accuracy of the breathalyser tends to follow price with the more expensive models having higher accuracy levels.
  • All the models that we stock are highly accurate provided that they are used and stored correctly, and re-calibrated correctly.
  • See our current digital breathalysers that we have for sale 

Re-calibration of digital breathalysers

A digital breathalyser will need regular re-calibration to make sure that it is retaining its accuracy.

How do you re-calibrate digital breathalysers?

  • For breathalyser models with a semiconductor sensor, this usually means simply purchasing a new breathalyser sensor about every 6 months, and fitting it yourself.
  • Some of the fuel cell sensor breathalysers including the Alcodigital Platinum also have a sensor which you can change easily yourself.
  • Models such as the Draeger 6820 breathalyser will require returning to a calibration centre.

Replacement sensors that you can easily fit yourself, are available for the following digital breathalysers:

Breathalyser terminology and information page last checked and updated 28/3/23

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