It’s never good when an alarm surprises you in the middle of the night.

I was recently on vacation with my family, and a weird beeping woke everyone up around 2 am. My wife thought it was a carbon monoxide detector. I thought it might be the baby monitor. It was actually a signal from a little sensor on the back of my arm prompting an app on my phone to go berserk. My blood sugar was low, and my fitness program was in jeopardy.

A few months ago, I started tracking everything I could about my health. In the dark bedroom of that vacation house, I was wearing smart rings on both hands and a smartwatch on my wrist. On my other wrist was a band that basically does the same thing as the smartwatch but without a screen. I’d been weighing myself with a body scanner and taking my blood pressure with a wireless cuff for weeks.

All this tech promised to tell me how well my body was working, but as I immersed myself in the alluring, sometimes dystopian future of health tracking, things got weird. Health trackers started as a way to keep a record of straightforward metrics, like the number of steps you take in a day; the industry has since matured into gadgets that promise to glean deeper insights into the essential functioning of your biological systems. Many of these new trackers take the data they collect and churn out a variety of scores — recovery scores, sleep scores, attention scores — to understand your body’s performance and give you benchmarks to chase.

My sharpening sense of mortality ultimately led me to explore the frontiers of health tracking to investigate my aches and strains — and maybe help me live healthier and longer.

The sensor on my arm was a continuous glucose monitor, or CGM, which is a wearable device that measures blood sugar. This kind of biosensor has long been a lifesaving tool for diabetic patients, but tech companies are increasingly marketing them to everyone in the name of “metabolic health.” One such company, Levels, was co-founded by Casey Means, a wellness influencer who is a central figure in the Make America Healthy Again movement and now the United States surgeon general nominee.

I am not diabetic. I’m also not an athlete, although I once was. I’m a tech journalist who, at the beginning of this year, started to feel quite old. Things that used to not hurt started hurting, and I felt tired constantly. Diabetes and heart disease, among the most prevalent chronic diseases in the United States, also run in my family, which made it seem wise to keep a closer eye on risk factors like my blood pressure and cholesterol.

My sharpening sense of mortality ultimately led me to explore the frontiers of health tracking to investigate my aches and strains — and maybe help me live healthier and longer.

What I can tell you is that over the course of my months-long experiment, covering my body with sensors and drowning my attention with fitness scores did occasionally make me feel better — when it didn’t make me feel worse.

Fitness trackers, as we understand them, have been around since the 1960s, when a Japanese company hoped to capitalize on the 1964 Tokyo Olympics by selling a pedometer called the Manpo-Kei — “manpo” means 10,000 steps in Japanese. The science behind that number has always been iffy, but the figure went mainstream in 2009, when the original Fitbit hit the market in the form of a thumb-size accelerometer that clipped onto your clothing.

Step-counting was only the beginning. In the early 2010s, tech companies flooded the market with fitness trackers. Apple released its health app in 2014 and then released the first Apple Watch the following year. That device used LED lights to measure your pulse, and eventually, Apple added sensors for your body temperature and electrodes to record electrocardiograms and track blood oxygen levels. Fitness-tracking became health tracking. The tracking devices themselves still performed the same basic measurements, but in the coming years, all of that data would get pumped through various algorithms to draw conclusions about your overall health. In theory, health-tracking software could spot — or even prevent — disease.

The amount of data that all of these devices collect is massive and extremely personal.

“For that to work, you have to have the largest data set on a person possible,” said Victoria Song, who covers wearables for The Verge. “But it’s pretty invasive, if you really think about it.”

The amount of data all of these devices collect is massive and extremely personal. Many devices need to know your age, height, and weight, not to mention where you are and how you’re moving at all times — which leads to heart rate, temperature, and blood oxygen readings. If you add a glucose monitor in the mix, health trackers can now get moment-to-moment updates about what’s happening in the fluid between your cells.

Safeguarding the sensitive health information these devices collect is a whole other challenge. The data is typically stored in the cloud. The privacy policies for these companies vary, but suffice it to say, it’s possible that data from your health tracker, probably anonymized, ends up in the hands of an advertiser. There have also been major data breaches involving health-tracking companies, including Fitbit.

Nonetheless, about 30 percent of Americans in one survey said they wear these kinds of........

© Vox