A growing number of bars and restaurants are stocking strips to test for the presence of fentanyl, Reuters reports.

A group called FentCheck regularly visits businesses in New York, Philadelphia, Oakland and San Francisco to distribute fentanyl strips. FentCheck provides instructions on how to use the strips. The results show up with lines indicating positive or negative, similar to a pregnancy or COVID-19 test.

“They are cheap, they are super easy to use and read and they give you a yes or a no that you can then use,” Dr. Kathleen Clanon, medical director of Alameda County, California, told Reuters. “They are very sensitive, meaning that the comparison tests have shown that they are likely to show fentanyl if it’s there and I’m comfortable with that as a community test.”

Some states consider fentanyl test strips to be illegal, the article notes. States including Alabama, Florida and Tennessee have introduced legislation to decriminalize the strips.