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Three reasons DUI breath tests might not be reliable

On Behalf of | Aug 28, 2023 | Criminal Defense, DUI Charges

If you have been charged with DUI in Pennsylvania, the prosecution will most likely use the results of a chemical breath test as evidence against you. This can be very powerful evidence. If your test showed a blood alcohol concentration (BAC) of 0.08% or higher, you are legally presumed too drunk to drive. For certain drivers, this legal limit is even lower.

Under Pennsylvania’s implied consent law, all drivers have consented to a chemical breath test in advance, as a condition of receiving a driver’s license. If you are pulled over on suspicion of DUI, you can’t refuse a breath test without facing consequences for it, including a license suspension.

It isn’t easy to avoid chemical breath test evidence, but it is possible to defend against it in court. The most common defense strategies involve attacking the reliability of the test evidence. These fall under three categories: issues with the driver, issues with the officer or issues with the device itself.

Issues with the driver

This strategy rests on the argument that something about the driver’s breath gave an inaccurate picture of their BAC when they blew into the breath test device.

For example, some studies have shown that a driver who has serious acid reflux may trigger an inaccurate BAC reading in a breath test device.

Other studies have shown that energy drinks and similar beverages may cause a driver to blow an inaccurate BAC reading.

Issues with the officer

An officer’s behavior in any traffic stop is relevant to a criminal defense. For instance, if officers overstep their authority in a traffic stop, they may violate a defendant’s constitutional rights. If a court determines that this happened, it may suppress the evidence obtained during the search.

In the context of a chemical breath test, the officer’s behavior is relevant to the administration of the test. The defendant must ask whether the officer was properly trained in the testing and if they administered the test correctly.

Issues with the device

Chemical breath test devices, such as the ones sold under the brand name Breathalyzer, are not perfect. Their manufacturers may promise that they are accurate, but independent studies have shown that they frequently are not.

One DUI defense strategy involves attacking the reliability of the chemical breath test itself. If the defendant can show that the device was not property calibrated or inherently unreliable, they can defeat one of the strongest pieces of evidence against them.