Students at a high school in Illinois will be randomly tested for alcohol this year, according to ABC News. The test uses hair samples.

Students at St. Viator High School in Arlington Heights have been randomly tested for drugs since 2007. All students are tested at the beginning of the year. Students are then randomly selected through a computerized system, using their ID numbers, throughout the year, and are tested again. This year, alcohol testing will be added.

According to Psychemedics Corp. of Acton, Massachusetts, which manages the school’s testing, the alcohol test requires 50 milligrams of hair, which is about the thickness of pencil lead. The company only began offering the test about a month ago.

“Particles of the drug or alcohol get trapped in the cortex of the shaft of the hair, so we test that and get back to the school in a short turnaround,” George B. Elder, the company’s Vice President of Schools and Colleges, told ABC News. “We can pick up on levels as low as two to three drinks a week on average for up to three months.”

The school will work with students who test positive for alcohol use, said Parents’ Club president Kathy Loy. After the first positive test, students will be given counseling, and tested again in 90 days. If the second test is also positive, the student will face disciplinary action.

The school has no legal obligation to report the test results to authorities, according to Sergeant Rich Sterando of the Arlington Heights police.

St. Viator is a private school. Public schools can only test students who are involved in extracurricular activities, said Edwin Yohnka of the ACLU of Illinois.