There are three types of tests that you probably think of when you hear “field sobriety test.” The first is your standard “do random acts” test. The second is a breath test. And the third is a blood test. Each of these tests are in the police’s arsenal for trying to determine whether a person is drunk or not. The police treat these tests as ironclad tests, when each one has its flaws and problems.

Take your “random tasks” field sobriety test. If you asked a sober person to walk in a straight line foot-over-foot, they would probably lose their balance at some point. In the context of a field sobriety test, a police officer could take this as a sign that you are drunk. But in reality, it is simply a hard task to perform unless you practice it. It is a ridiculous test that doesn’t necessarily prove if you are drunk or sober, and yet it is championed as such.

Then there is the breath test, or a Breathalyzer test. These tests have been criticized as lacking in precise accuracy, and there have also been challenges to breath test results when the police officer failed to follow the instructions for implementing a breath test as told by the device’s manufacturer.

The blood test can also be botched, but this usually only happens when a testing facility is negligent or a lab technician botches the test, either by tainting the evidence or improperly performing the test.

There’s no guarantee that the evidence against you is inadmissible due to any of these mistakes — but the police aren’t perfect.