It’s a good thing that more and more people are using wearable technology devices to maintain their fitness and track their health data, but users should realize that the companies selling these products are likely selling their personal health data, according to one senator.

Sen. Chuck Schumer, D-N.Y., said at a news conference Sunday that Americans could be unwittingly entering into a “privacy nightmare” by forfeiting their information to FitBit and other wearable health trackers. He pressed the Federal Trade Commission (FTC) to examine whether technology companies are selling data (including the number of steps users take in a day, their heart rates and caloric information) to third-parties.

“Personal fitness bracelets and the data they collect on your health, sleep, and location, should be just that – personal. The fact that private health data – rich enough to identify the user’s gait – is being gathered by applications like FitBit and can be sold to third-parties without the user’s consent is a true privacy nightmare,”  he said in a statement.

“The FTC should require fitness devices and app companies to adopt new privacy measures that will help conceal the identity of individuals and develop policies to protect consumer information in the security breach,” he said, adding that the FTC “had openly voiced its concern about the selling of personal fitness data between companies, but has yet to take action to push application developers and other fitness monitoring companies to provide an opt-out opportunity.”

A FitBit spokesperson told Business Insider that the company, which manufactures sophisticated bracelets and belt clips, does not sell users’ information to third parties.

Schumer’s warning comes one week after the senior senator from New York called on the Federal Aviation Administration to speed up regulations for private drone use, citing a number of recent accidents in New York City as proof that -- as with wearable fitness trackers -- consumers simply need more information.

“We want to make sure two things are not interfered with with these drones,” he said, “one is safety and the second is our right to privacy.”