To determine if a person is driving under the influence of alcohol, traffic officers conduct a **breathalyzer test**. This test involves blowing into a device that measures the amount of alcohol in the blood. If the result is positive, the test is repeated to confirm it. However, even if the first test is negative, officers may conduct a second test if the person **shows obvious signs of having consumed alcohol**. This is because visible symptoms may indicate that the driver is affected, even if the device did not initially detect it.

Additionally, alcohol and drug detection tests are mandatory for drivers who show symptoms of being under their effects, have been involved in an accident, have committed traffic violations, or during preventive checks. Refusing to take these tests can result in fines and penalties.

Therefore, a second breathalyzer test may be conducted if there are **clear signs of alcohol consumption**, even if the first test was negative.