How does an alcohol screening test workour suresign alcohol screening test rapidly detects the presence of alcohol in the exhaled breathampnbsp if alcohol is present in the exhaled breath it reacts with the chemically coated crystals and produces a colour changeampnbsp the test provides relative blood alcohol concentration at 005how long after alcohol consumption can i use the test you should wait 15 minutes after your last alcohol consumption or drink a glass of water before taking the te