Last week, life insurance company John Hancock Financial announced that it would only sell so-called interactive policies that allow customers to share fitness data in exchange for discounts. Though customers can opt out of the program, the 156-year-old company’s decision has created worry about privacy precedents and unintended consequences.

Broadly speaking, “interactive policy” means the company receives extra data and then uses it to adjust premiums or give discounts, according to a spokesperson from the National Association of Insurance Commissioners. These policies are frequently used in the United Kingdom and are becoming more popular in health insurance and with individual companies, but one of the most well-known examples comes from car insurance. Companies like Allstate frequently strike a deal with interested drivers: install a monitoring device in your car and, if you’re a safe driver, receive a discount in return.

The additional data elements we’re talking about is pretty small and inconsequential compared to the data we already have

For insurers, this seems like a win-win since both customers and life insurance companies want the customers to live longer. “The life insurance industry is the most logical setting for wellness,” says Brooks Tingle, president and CEO of John Hancock Insurance. “We have relationships with customers that average 20 years and we make no bones about the fact that we stand to benefit if our customers live longer.” This feature will likely bring healthier people to the company, too, because people who are already active are more likely to be attracted to the option of discounts if they meet predetermined goals. (John Hancock only offers discounts; they don’t change the original premiums.)

At John Hancock, customers can earn discounts in many ways, including taking online nutrition classes, going to the doctor, and, of course, wearing a tracker and meeting predetermined fitness goals. The fitness option is compatible with most major trackers, users can receive a free Fitbit, and the policy has been very popular since it debuted in 2015, says Tingle.

Still, experts worry about privacy and liability. How much information is being shared, and who is responsible for verifying accuracy? If the data shows a health problem — like a heart arrhythmia — who is responsible?

Tingle stresses that the customer chooses how much data to share and that John Hancock won’t share it with third-party companies. “So your wearable may track six things, but you might just want to share steps or calories,” he says. (The minimum data shared seems to be steps taken.) He points out that life insurance companies are already privy to much more sensitive data anyway, such as medical files and doctors’ notes. “The additional data elements we’re talking about — things like steps taken or whether you took an online nutrition course — is pretty small and inconsequential compared to the data we already have,” he adds, noting that the fitness data will be protected in the same way as other sensitive data.

There is also the question of method. Many fitness trackers are not accurate at measuring heart rate, and can backfire when it comes to weight loss. It’s easy enough to cheat with fitness devices, but John Hancock isn’t worried about that either. “These programs are going to be in place for an average of 20 years and often much longer,” Tingle says, “and while people might figure out a way to get more steps in the short term, people aren’t going to do that for two decades.”

Though the program is optional, experts worry that it’ll change down the line. “At this stage, they’re saying it’s voluntary,” Ann Cavoukian, who served as Ontario’s Information and Privacy Commissioner until 2014 told CBC.”My gut says over time it’s not going to be voluntary, or it will be less voluntary, or there will be consequences for not doing it. Like you’ll pay higher premiums because … you’re not willing to share that data. That’s what disturbs me.” (For his part, Tingle stresses that it’s important “the customer has total choice about whether they participate.”)

Another worry is that this will fundamentally change how we measure our lives, according to Dan Bouk, a historian at Colgate University. Bouk studies bureaucracy and quantification and is the author of How Our Days Became Numbered: Risk and the Rise of the Statistical Individual. At the turn of the 20th century, he explains, corrupt practices tarnished the reputation of US life insurers. As a result, many, including Metropolitan Life, responded by developing and instituting “life extension” programs to seem more philanthropic. These companies took techniques developed for assessing life insurance risk — annual medical examinations, blood pressure measurements, height-weight tables — and made them standard parts of our lives.

“Some historians have shown that most doctors don’t even have scales in their offices until they’re required to by life insurance companies,” he says. “Before this era, most people are only getting a health examination if they’re buying life insurance. Out of a seeming moment of weakness, when companies were under political pressure, they developed new forms of power in terms of shaping how we think about our bodies.”

Medical examinations and screenings certainly seem useful. But they have also “made many people think they were unhealthy in moments that they weren’t, and sacrificed a great deal of human individuality,” Bouk says. For example, many doctors now argue that we use too many medical tests and researchers have long argued that “accepted knowledge” about height-weight tables and obesity are wrong.

“My concern is that you give this power to someone who is giving you life insurance — and life insurance is a crucial means of protecting you and your family against unforeseen accidents — then they get to decide what your healthy life looks like, even if we decide that’s not how a healthy life should look,” Bouk says. “They impose and flatten the variety of ways in which it’s acceptable to be healthy. I can only imagine that certain types of yoga might not work well with an activity tracker.”