The Best Health Trackers in 2026: ECG, AFib, SpO2 and Skin Temp

A reader emailed us last spring asking which Garmin Forerunner was best for “health tracking.” We suggested he might not actually want a Forerunner — that what he was describing (his father had paroxysmal AFib, he wanted to keep an eye on his own rhythm, he had no interest in marathon training) was a different shopping problem altogether. He bought a Withings ScanWatch 2 and now wears it under a shirt cuff to client meetings.

That email is the reason this article exists. “Health tracker” and “fitness tracker” have collapsed into a single category in most reviews, and it is the wrong taxonomy. The devices that win on workout data — Garmin Forerunner, Coros Pace, Polar Vantage — are not the devices that win on cardiac and metabolic data. The reverse is also true. If you came to this page wanting ECG, AFib screening, blood-oxygen trends, skin temperature, and HRV, the fitness tracker roundup is not where you should be.

What follows is five picks, ordered by how well they handle the specifically medical-adjacent sensors. Some of them are wrist watches, one is a ring, one is a bathroom scale. They share a sensor philosophy rather than a form factor.

What counts as a “health” sensor

The line we draw here is whether a sensor produces a signal that a clinician would also be reading, and whether the device has a regulatory clearance to make a screening claim about it. Five sensor categories matter:

• Single-lead ECG. The wrist-and-finger electrode pair that records a Lead I rhythm strip. Used for screening atrial fibrillation between visits.
• Optical blood-oxygen (SpO2). Red and infrared LEDs measuring oxygen saturation. Useful for trend lines and sleep apnea suspicion, not for clinical hypoxia decisions.
• Skin temperature. Continuous overnight temperature, usually as a deviation from a personal baseline rather than an absolute number. Picks up fever, ovulation, and (sometimes) illness onset.
• Heart-rate variability (HRV). Beat-to-beat variation in RR intervals during sleep. A noisy signal individually, but the trend correlates with autonomic state. We have a longer explainer on HRV for anyone new to it.
• Irregular-rhythm notifications. A background algorithm that watches PPG traces and pings you when something looks like AFib. Distinct from the user-initiated ECG; this one is always-on.

A workout-focused tracker may have one or two of these. A health-focused tracker has most of them. The best ones also have FDA 510(k) clearance for the cardiac claims they make, which matters because the regulatory file forces the manufacturer to publish accuracy data against a 12-lead reference. That data is sometimes inconvenient, which is the point.

The picks

1. Withings ScanWatch 2: best overall

The ScanWatch 2 wins the category because Withings is, frankly, the only consumer brand whose product roadmap reads like it was written by a medical-device company that also designs watches, rather than the other way around. The TempTech24/7 sensor is a genuine generational step. Overnight temperature curves with 0.1°C precision are something we have not seen elsewhere outside of research-grade rings, and the ECG path is well validated. We have the longer ScanWatch 2 review for anyone who wants the detail.

The compromise you make is the screen. If you grew up on an Apple Watch, the small OLED is going to feel cramped. The trade is that the battery lasts a month, which means the device is on your wrist when the cardiac event happens, instead of on the charger. For health tracking specifically, that uptime calculation is the whole game.

A note on accuracy. Wrist ECG cleared by the FDA is validated against a 12-lead reference for rhythm classification (AFib vs. sinus rhythm vs. inconclusive). It is not a substitute for a Holter monitor and it cannot screen for the dozens of arrhythmias a cardiologist might be looking for. We get into the limits in our ECG-smartwatch explainer.

2. Apple Watch Series 9: best for iPhone users

The Apple Watch is the device people already own, and on cardiac features it is genuinely at the front of the category. AFib History, which estimates the percentage of time you spent in fibrillation over a rolling seven-day window, is the most ambitious consumer arrhythmia feature shipping today, and the underlying ECG was the first to get the original FDA clearance back in 2018.

There are two reasons it does not win the category. The first is the battery. Eighteen hours is fine for a smartwatch; it is poor for a sleep- and overnight-temperature-tracking device, because charging has to happen during one of the two windows the device is most useful. The second is the SpO2 disablement. Apple shipped a hardware blood-oxygen sensor for years, and in January 2024 turned the software off on new US units in response to the Masimo injunction. The hardware is still in there; Apple just legally cannot use it on US-sold devices. We covered the broader story in our SpO2 wearables piece; the short version is that if SpO2 is the metric you care most about, the Apple Watch is the wrong choice in the US specifically.

Everywhere else, it is the best smartwatch you can put on an iPhone user, and for cardiac data it is one of two devices we trust.

3. Fitbit Charge 6: best budget option

The Charge 6 is the answer to “I want the same sensor stack as the ScanWatch for half the price.” It is not the same stack. The temperature signal is coarser, the ECG accuracy is comparable but not better, and the battery is a week instead of a month. But everything is there. ECG, SpO2, skin-temperature variation, HRV trend, irregular-rhythm notification, all in a $159 band.

Fitbit Premium is the rub. The raw sensors are free. The Daily Readiness score and the more elaborate sleep profile sit behind a paywall, which feels mean when the underlying data is already on your wrist. We can live without Premium; most of the cardiac data is the part you would not subscribe for anyway. But the upsell on the home screen is constant. For deeper context on what each of these temperature signals actually means, our skin-temperature wearables explainer covers the methodology.

4. Oura Ring Gen 3: best for continuous baseline

We rank Oura fourth, not lower, because for the specific use case of overnight physiology baseline (what is your temperature doing across a month, how is your HRV trending, are you getting fewer hours of deep sleep than you did in January), it is the best instrument you can buy without a research budget. The de Zambotti validation paper holds up; Oura’s own subsequent work has been published, not just marketed. We compare Oura against its peers more directly in the sleep tracker roundup.

It is fourth because the ring cannot record an ECG, which is the headline feature of this category, and because the subscription model is the kind of thing that turned the original Basis Peak owners off the modern market in the first place. Withings, Apple and Fitbit will all give you most of your data without paying monthly. Oura will not.

A note for prospective buyers eyeing the Gen 4: we have been wearing one for several months now, and while the SpO2 path is genuinely improved, the differences from the Gen 3 are not large enough to recommend paying more right now. The Gen 3 is the value pick in the line.

5. Withings Body Scan: honorable mention

We include the Body Scan because it is the only consumer device on the market that gives you a multi-lead ECG with the same casual cadence as a daily weigh-in. Six leads versus the wrist watch’s one is a real difference. More leads catch more of the morphology a cardiologist would actually look at, and the segmental bioimpedance, while not laboratory-grade, is the closest a household device gets to a DEXA scan.

It is an honorable mention rather than a top pick because it is not a wearable. The data is daily, not continuous, and the device cannot catch an arrhythmia that happens at 3am while you are asleep. The right way to think about the Body Scan is as a complement to a wrist or ring device, not a replacement, and that is why it sits at the end of the list.

How accurate are these sensors, really

The honest answer is “less accurate than the marketing, more accurate than skeptics expect, and good enough to be worth wearing if you understand what you are looking at.” We have a longer write-up of the literature in our wearable sensor accuracy piece, but three things worth flagging here:

ECG. The FDA-cleared single-lead ECG devices are validated for rhythm classification specifically: sinus vs. AFib vs. inconclusive. Their published positive-predictive values for AFib are in the 80-90% range against a Holter monitor reference, with sensitivities in a similar range. That is good enough to be useful as a screening tool and not good enough to be a diagnosis. A “normal” reading does not rule out paroxysmal AFib that simply did not happen while the watch was on.

SpO2. Wrist SpO2 readings tend to read a few percentage points lower than fingertip pulse oximetry, with more variance. The Sjoding et al. 2020 NEJM paper documented systematic overestimation of saturation in patients with darker skin pigmentation, an issue the FDA acknowledged in updated 2023 guidance for pulse oximeter manufacturers. Treat the wrist SpO2 trend as directional, not absolute.

Skin temperature. Wrist and finger skin temperature is not core body temperature. It tracks core temperature loosely overnight, when you are still and the limb is at thermal equilibrium with the environment. It does not track core temperature during the day. The useful signal is the deviation from your own baseline, not the absolute number.

HRV. Consumer HRV is a noisy single-night signal that becomes meaningful as a weekly or monthly trend. Comparing your HRV to your friend’s HRV is mostly meaningless; comparing your HRV to your HRV from three months ago is meaningful. The methodology varies across vendors (RMSSD overnight on Oura, time-domain root-mean-square during the day on Apple Health, vendor-specific weighted averages on Garmin and Fitbit), so do not cross-compare devices either.

What we would actually do

For most readers who came to this page because they care about heart-health features specifically, the answer is the ScanWatch 2, with the Charge 6 as the budget alternative. If you live in iMessage and refuse to wear two watches, the Series 9. The Oura is a complement to either of those, not a replacement. The Body Scan is for a household, not for a person.

The interesting thing about this category compared with the fitness tracker category is that the cardiac sensors have pulled away from the workout sensors over the last two years. Optical HR has plateaued. Most reputable trackers now hit the same accuracy on a steady-state run. ECG, AFib history, skin temperature and SpO2 have not plateaued, and the cleared devices are visibly better than the uncleared ones. If you are buying for the medical-adjacent reasons, that gap is where to spend your money.