Details
To Perform a test with the Express Check® Breath Alcohol Test, the user squeezes the tube to crush the ampoule in the test, and then blows into the appropriate end of the test for 12 seconds. Yellow crystals remain unchanged if alcohol is not present at the test's threshold. Alcohol in the breath turns yellow crystals to a pale blue or green colour within two minutes if the concentration meets or exceeds the test's threshold. 
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