How to use Redlines

We understand that ON FIRST-TIME USE you may think that the Redline device is a little fiddly to use.  They’re NOT!  If you read the instructions carefully and follow them correctly, you’ll see that Redlines are actually very simple!

Instructions For Use

  • Before consuming alcohol, read and ensure you understand the ‘Instructions’ and ‘Interpretation of Results’, and the products’ ‘Disclaimer’.  They’re on the leaflet inside the product’s packaging, and on the unit’s breath bag.
  • Do NOT carry out a Redline test within 20 minutes of your last drink of alcohol (or use of a mouthwash, gargle or other product containing alcohol)
  • Use a tester within 5 minutes of opening the tube (i.e. snapping off the end caps).
  • Ensure that you evaluate the results UNDER GOOD LIGHTING CONDITIONS.


  • Snap off the ends of the red and white caps at the end of the tester tube, and then shake out and discard the small amount of white crystals that are loosely contained within the tube.

(These white crystals are harmless silica gel, used to keep the yellow active chemical crystals dry).



  • Using ONE continuous breath, fully inflate the bag.

(More than one breath will deliver an inaccurate result).

Blow in bag.JPG


  • Insert the WHITE cap end of the tester into the WHITE neck of the fully inflated bag.

(Alternatively, note that there’s a red arrow on the tube.  This shows the direction of the airflow out of the bag through the tube, and so it should be pointing AWAY from the bag).



  • Using both hands, squeeze the bag slowly and evenly, so that ALL the breath contained in the bag is expelled through the tester tube.  This should take approximately 30 seconds.

(Note that it is entirely normal for the tester tube to warm up during this operation.  This is simply an effect of the chemical reaction taking place between the expelled breath reacting with the yellow chemicals).



  • Evaluate the results under good lighting conditions.  Results are best visible after approximately 2 minutes of taking the test.



An ‘UNDER THE LIMIT’ result.


If you are under the limit, there is no ‘greening’ of the crystals, or the progression of the green colour change has not reached the red line.

  • This test result indicates that you are currently under the legal limit, but remember that the result is not definitive and cannot be used for legal evidence.
  • If you are taking the test immediately following consumption of alcohol, you should NOT decide to drive based on a single 'under the limit' result.  It is possible to deliver an ‘over the limit’ result some time after producing an ‘under the limit’ result because alcohol takes up to 2 hours to become fully ingested prior to its dissipation.  Use of a second tester a short while after the first in the same manner as described above is therefore strongly encouraged in these circumstances. 
  • If you are using a tester 2 hours or more following consumption of alcohol, an 'under the limit' result will provide accurate and reliable (but NOT evidential) guidance to your decision whether to drive immediately thereafter.  Use common sense and your discretion!  



An ‘OVER THE LIMIT’ result.


If you are over the limit, a distinct green colour change will have occurred in the yellow crystals and progressed all the way up to the red line or beyond.

  • You SHOULD NOT drive a motor vehicle
  • Unless you can make alternative travel arrangements, it is strongly recommended that you WAIT a reasonable period to allow the alcohol you have consumed to dissipate sufficiently to produce an ‘under the limit’ result, and then use a second tester in exactly the same process as above to see if this has been achieved.
  • If you do not have a second tester, note that it can often take a considerable period for ingested alcohol to dissipate to levels below the legal drink-driving limit – particularly if the consumption was excessive.  Such periods can vary widely from person to person.  With any doubt whatsoever, YOU MUST NOT DRIVE A VEHICLE.

Dispose of testers, discarded crystals, end caps and breath bags in a responsible manner immediately after use.