Wearables and Continuous Health Monitoring

Smart rings, watches and glucose patches now track heart rate variability, sleep, blood oxygen and glucose around the clock. Here is what the numbers can and cannot tell you, and who sees them.

A decade ago a fitness tracker counted your steps and called it a day. The devices people strap on now do something different: they record a stream of physiological signals around the clock, then turn that stream into daily scores for readiness, recovery, sleep and, increasingly, blood sugar. The shift from counting movement to monitoring biomarkers is what has turned wearables from gadgets into a serious consumer-health category, with smart-ring maker Oura valued at $11 billion after a 2025 funding round and Whoop close behind. The data these devices produce can flag real problems and reveal useful trends, but its accuracy varies by metric and by device, and most of it sits outside the privacy rules that govern your doctor’s files. Here is what the technology actually measures, who the major players are, and what the numbers are good and not good for.

From step counts to continuous biomarkers

The defining feature of the current generation is continuous, passive measurement. Instead of a single reading, devices sample heart rate, heart rate variability (the small beat-to-beat timing changes that reflect autonomic nervous-system balance), skin temperature, blood oxygen and sleep stages throughout the day and night. Most of this comes from photoplethysmography, the green-light optical sensor that reads blood flow at the wrist or finger.

That continuous signal is what lets a ring or band tell you your resting heart rate is creeping up, your overnight HRV has dropped, or your sleep was unusually fragmented. The appeal is trend-spotting over time rather than one-off snapshots. It is also why the category has expanded beyond athletes: the same sensors that gauge training recovery can surface early signs that you are run down or fighting an infection.

The major players

Oura built the smart-ring market and remains its largest name. The company raised more than $900 million in a Series E round that valued it at $11 billion, roughly doubling its $5 billion valuation from late 2024, CNBC reported. Oura said it had sold more than 5.5 million rings since 2015 and expected to reach $1 billion in sales in 2025, according to the same report.

Whoop, the screenless subscription band favored by athletes, closed a $575 million round at a $10.1 billion valuation, the company announced. Its newer hardware added an ECG feature that received FDA 510(k) clearance, per coverage compiled by Sacra.

Apple and Garmin anchor the watch side. Apple’s most consequential moves have been regulatory: its Apple Watch sleep-apnea detection feature received FDA clearance in September 2024, TechCrunch reported, joining an ECG function cleared back in 2018 and irregular-rhythm notifications that can flag atrial fibrillation. Notably, Apple removed blood-oxygen readings from US watches in late 2023 after losing a patent dispute with Masimo, then restored the feature in 2025 by processing the data on a paired iPhone, the same coverage noted. The episode is a reminder that even flagship features can vanish over litigation.

The push into consumer glucose

The biggest frontier is blood sugar. Continuous glucose monitors, long prescribed for people with diabetes, went over the counter in 2024. The FDA cleared Dexcom’s Stelo as the first OTC glucose biosensor, and Abbott’s Lingo followed soon after, both reaching the market without a prescription, as MedTech Dive reported. Abbott launched Lingo in the US in 2024 priced from roughly $49 for a single sensor, CNBC reported.

The positioning differs in a telling way. Stelo, built on Dexcom’s G7 platform, is aimed at adults who do not use insulin, while Abbott has marketed Lingo explicitly as a wellness biowearable rather than a diabetes product. That wellness framing matters because the value of glucose data for people without diabetes is still debated. Seeing your blood sugar spike after a meal can be a powerful behavior cue, but researchers caution that normal glucose swings are not in themselves a sign of disease. The rise of consumer CGMs sits alongside other metabolic-health trends, including the GLP-1 weight-loss drugs that have reshaped how people think about food and metabolism.

What the data is good for, and what it is not

Independent validation studies are blunt about the limits. A 2025 study in Physiological Reports found wearables vary widely in measuring nocturnal resting heart rate and HRV against single-lead ECG, with some devices showing strong agreement and others performing poorly, per the published findings. Sleep is shakier still: a multicenter validation study reported that consumer trackers tend to overestimate sleep by misclassifying brief wake periods, and accelerometer-plus-heart-rate sleep staging reaches only about 60 to 70 percent agreement with polysomnography, the clinical gold standard, according to research published in JMIR mHealth and uHealth.

The practical takeaway is that wearables are better at tracking your own trends than at delivering clinical-grade absolute numbers. A rising resting heart rate or a falling HRV over weeks is a meaningful personal signal; a single night’s “deep sleep” figure is closer to an estimate. The strongest case is for the FDA-cleared alerts, such as irregular-rhythm and sleep-apnea notifications, which are designed to prompt a doctor’s visit rather than diagnose on their own. None of it replaces clinical testing, a point that connects wearables to the broader move toward functional and preventive medicine and to research-grade tools like epigenetic clocks that measure aging in a lab.

The privacy question

The less visible issue is who else sees the data. Health information generated by consumer wearables generally falls outside HIPAA, because that law covers data held by clinicians and insurers, not gadget makers. Legal analysts note that much wearable data is left largely unregulated and can be shared or sold under terms users rarely read, as a peer-reviewed review in the journal Cryptography detailed. The Federal Trade Commission has tried to narrow the gap: its amended Health Breach Notification Rule, effective July 2024, extended breach-disclosure duties to many health apps not covered by HIPAA, and several states have begun treating biometric and inferred health data as sensitive, per analysis from Coblentz Law. For now, the protections depend heavily on a company’s own policies.

FAQ

Are consumer wearables accurate enough to trust? It depends on the metric. Heart rate and resting heart rate trends are reasonably reliable on better devices, while detailed sleep staging and HRV are noisier and vary by brand, according to validation studies in Physiological Reports and JMIR mHealth and uHealth. Treat the numbers as trends rather than diagnoses.

Should someone without diabetes use a continuous glucose monitor? Over-the-counter CGMs like Stelo and Lingo are now available without a prescription, and some people find the feedback useful for changing eating habits. But researchers caution that normal glucose fluctuations are not a sign of disease, and the long-term health benefit for non-diabetics is not yet established.

Is my wearable health data private? Often less than people assume. Data from consumer devices generally is not covered by HIPAA, so protection depends on each company’s terms of service, though the FTC’s 2024 breach rule and new state laws have started to add safeguards.