Do they sell alcohol testers in supermarkets?

No.

Alcohol tester is a professional instrument to detect the alcohol content, used for the police, traffic management departments and other institutions to carry out DUI testing. When you buy it, you should choose formal channels, medical equipment stores or specialized testing technology companies and so on. These places have the qualification and ability to sell and provide related services, and can ensure that the purchased product meets the relevant standards and legal and regulatory requirements.