The U.S. Food and Drug Administration warned consumers this week against using a phone or tablet exclusively in concussion diagnosis.

“Products being marketed for the assessment, diagnosis, or management of a head injury, including concussion, that have not been approved or cleared by the FDA are in violation of the law,” said Jeffrey Shuren, director of the FDA’s Center for Devices and Radiological Health, in a statement. If the FDA takes action against specific companies or devices though warning letters, it will post them publicly, according to Popular Science.

All systems used to help assess head injuries, such as the imPACT test, which includes various cognitive and other tests performed on a tablet or computer, require the input of a medical professional. Another FDA-approved device, the Brain Injury Adjunctive Interpretive Oculomotor Assessment Aid, is an eye-tracking tool that assesses brain condition.

Related: New Concussion Device Gets FDA Approval

Unapproved devices or applications — which are easy to find in the iPhone App Store — are tempting to people working the sidelines of sporting events because they might claim to offer answer more quickly, says Kenneth Podell, director of the Houston Methodist Concussion Center. "They're looking for the shortest, quickest, easiest thing," Podell told Popular Science. "They might not question if it's valid or not."

Unapproved tools that might not be as accurate can be dangerous. “The biggest danger is a false negative," Podell says, "meaning the test says there’s no concussion when there actually is one.”

False positives — identifying a concussion when there isn’t one — isn't as harmful in the immediate aftermath of a head impact, says Podell, who adds that they also cause problems. "If you keep diagnosing someone with a concussion when they don’t have one it alters their playing time, or academics."

Podell stresses that there are no devices or tools that can diagnose a concussion on their own. "The tools we do have available are absolutely helpful," he says, and they're able to assist experienced athletic trainers in identifying athletes who should leave a game, or who need more rigorous evaluation. "But that's because we're using multiple different tools — no one tool is 100 percent."

Paul Steinbach is Senior Editor of Athletic Business.