Amazon is developing a health device that can read human emotion, according to Bloomberg. The idea is that such a device might be able detect mental health issues. Comcast is working on an in-home device that might sense when people fall or are going to the bathroom an unusual number of times (which can be a sign of an underlying health problem). These are just the latest examples of Big Tech’s forays into the giant health care market. Apple and Microsoft are investing, too.

Health care makes up a whopping one-sixth of the U.S. economy, so it’s no surprise the likes of Jeff Bezos and Tim Cook would like a slice.

Jeff Becker, an analyst at Forrester, says big tech knows a lot of Americans are unhappy with the quality and cost of their health care.

“The tech industry can smell blood in the water,” he said.

But there are risks for tech companies that want to sell us devices to monitor our pulse, detect when we fall or are feeling depressed. That comes down to how they safeguard and treat personal health data.

“Some of the big institutions in health care are still highly trusted, but the least-trusted entities are tech companies right now,” said Bill Evans, managing director of Rock Health, a research and investment firm.

If a tech company were to accidentally or intentionally reveal personal health data, it would face even bigger trust issues.