If 10 years ago, you wanted to know whether the people around you were tracking their health, there would be some dead giveaways. You could check their wrists for an Apple Watch, Fitbit, or Nike Fuelband. Today, it might be harder to tell. Sure, smartwatches and smartbands are alive and well, but a multitude of other designs have entered the market.

Continuous glucose monitors (CGMs) hide behind shirt sleeves. Smart rings, earrings, bracelets, and even necklaces blend in with regular accessories, and fitness bands disappear against neutral fabrics to match an outfit. The makers of these discreet trackers want them as invisible as possible. Through hardware and software advances, companies are building the next generation of wearables that are even lighter, smaller, more capable, and less visible than the last.

We've been hearing about the "quantified self" for nearly two decades as devices to track our steps have evolved to give us health data that used to require a trip to a clinic and cost thousands of dollars. We explore how that health data actually impacts your life, whether you're walking into your next doctor's appointment or forgetting about the sensor sitting on your wrist.

"Over time, we've noticed that these products have gotten smaller," Forrester principal analyst Arielle Trzcinski said about health wearables in an interview with ZDNET.

Tech companies have always been in the business of optimizing for size. Apple's first MacBook weighed 5 pounds. The latest model weighs half that. But while phone companies are shipping bigger smartphones with massive screens and trifoldable designs, the accessories that connect to these phones have miniaturized.

So, how did these devices go from bulky and branded to indistinct and invisible? And why?