To get the most from your personal breathalyser, use it regularly to monitor the change in your level of intoxication, rather than looking at a single specific reading.

Always wait at least 15 minutes after drinking or smoking (or you risk damaging the sensor) and then test yourself, trying to blow steadily and consistently. Take 3 tests, each approximately 2 minutes apart and compare the readings. If one is substantially different to the other two, try once more. When you have three readings that are within a reasonable difference of each other, take an average and wait 30 minutes – then test again. Don’t be surprised if the reading is not exactly the same every time. Carry on testing every 30 minutes until you get a zero reading. You may well find that the reading initially INCREASES, between the first few tests and the next – this is because it takes time for the alcohol to be absorbed into the blood stream from your stomach. You will also probably find that the level does not drop by the same amount every half hour – and this is one of the main reasons for buying a breathalyser, to see how YOUR body reacts and how long it takes to absorb the alcohol. You can repeat the test the ‘morning after’ to ensure that the alcohol has left your system and you do not find yourself still over the limit.

You can use our guide to units of measurement to get some idea of how your readings compare, but if you intend to drive – do NOT drink! The only safe limit is zero.