Startup Empatica says its Embrace smart watch is now approved by the US Food and Drug Administration as a medical device—a rare designation for a wearable.

Winning approval: The $249 watch detects when a wearer is having a convulsive seizure and lets family members know via a smartphone app. In a 135-patient trial as part of the FDA approval, epilepsy patients suffered 40 seizures, and the watch’s algorithm spotted them all.

Why it matters: There are 3.4 million people in the US with epilepsy. Worldwide, the figure is roughly 50 million. Keeping track of when seizures happen can help get patients medical attention and aid doctors in monitoring their condition over time.

What it means for wearables: The approval allows the firm to make medical claims about the device, and could enable people with epilepsy to have insurance pay for it. It may also encourage doctors and hospitals to use such devices, says Rosalind Picard, Empatica’s cofounder and chief scientist.