There are many urban myths about how to fool breathalyzers, and 99% of them are false. When people try to fool the machine, they usually end up getting charged with refusal to submit to a breath test and DUI. The machines are built to detect most of these tricks, and the officers have seen them all before.
However, there is a right way and a wrong way to blow into a breathalyzer. When someone has been drinking, there is more alcohol in the bottom of that person’s lungs than there is at the top of the lungs.
Studies have shown that a driver who holds his breath before blowing into a breathalyzer will increase the BAC reading by 15.7%, while a driver who hyperventilates will decrease his BAC result by 10.6%. That is a 26.3% difference.
The police want you to take a great big breath and blow really hard, so that you exhale as much of that alcohol-rich air in the bottom of your lungs as possible. Do not fall for it.
Most breathalyzers require about seven seconds of uninterrupted breath, but they do not require the person to blow hard. Blow as you would normally blow through a straw, not as if you are trying to blow up a balloon. If you have any conditions that stop you from blowing steadily at normal pressure for at least seven seconds, notify the officer before taking the test.
Do not hold your breath or take a big breath before blowing. The less time the air has spent in your lungs the less alcohol will transfer from your blood to your breath. Just blow continuously at a normal pressure until the officer tells you to stop.
Also, try to be cooperative and friendly with the police. Many people mess up at least one of their breath tests, and the police officers will usually give people several chances to do it right before the officers charge them with refusal to submit to a breath test. Drivers who are rude and belligerent tend to get many fewer chances.