This one, in particular, detects the drug through the saliva from job applicants or employees. These tests are also known as saliva tests or oral fluid tests. A mouth swab test is usually done to identify recent drug use within a few hours or days (2-3). Many employers use mouth swab tests over others because of how simple and noninvasive they are. You can click here to learn more about these tests and how to pass a drug test effectively.