The prehospital care provider has been limited in his or her initial assessment of patients due to having available only a limited number of simple diagnostic tests. There has not been an accurate field test available to rule out significant ethanol intoxication. We designed a prospective trial for the prehospital setting to test the utility of a rapid, semi-quantitative, saliva alcohol reagent strip for patients with an altered level of consciousness. We found that these strips were useful in ruling out significant ethanol intoxication as a cause of an altered level of consciousness with a sensitivity of 85.7% and a specificity of 94.4%, but were not useful in accurately predicting the blood alcohol level. We conclude that these reagent strips are useful in the prehospital setting to provide information about patients with an altered level of consciousness.