I Tested the New Heart Rate Sensor in the Apple Watch to Find Out If It’s Really Better Than the Garmin One.
Apple caught my attention with the claim that the Apple Watch Series 12 and Ultra 4 have “the most accurate heart rate sensor ever in a wearable.” Creating a truly accurate heart rate sensor is difficult, and in my experience, Apple doesn’t have a great reputation in this area. So, I’ve been testing the Series 12 quite extensively over the past week, and now I have the results.
I’m very picky about accuracy; long-time readers have seen me test watch after watch, comparing the readings to my trusty chest strap to find out how good each one really is . Sometimes this brings surprises: for example , the Powerbeats Pro 2 is surprisingly poor at tracking heart rate if you have small ears. I also found the Garmin Forerunner 570 to be surprisingly accurate at measuring heart rate, far better than any other device I’ve tested so far. (The Garmin Forerunner 970 and the newest Fenix and Venu watches share the same sensor.)
What Apple says about its heart rate sensor and why I doubted it.
Is the new Apple Watch really good enough to beat Garmin’s best sensor? Apple thinks so, but I doubted that claim for several reasons. First, there’s simply Apple’s track record. Early Apple Watch models had sensors better than most wearables of the time, so Apple earned a reputation for making highly accurate devices. For example, around 2019, the Series 4 performed much better for me than the Whoop 3.0. But time goes on, and devices get better. Garmin has an excellent sensor, as I’ve already explained; the Pixel watch is also impressively good. But Apple simply couldn’t keep up.
You can see this by comparing my results over the years: the Series 11 is buggy, while the Garmin is excellent, and the Series 10 struggles compared to the Fitbit Charge 6. If I were to rate the accuracy of every heart rate monitor I’ve tested, the Garmin 570 would get an A, the Pixel Watch and most good fitness watches would get a B, and the Apple Watch (Series 10 and 11) would get a C. (An S would be reserved for chest straps.) Not long ago, I was downvoted for a Reddit comment that Apple’s heart rate accuracy (pre-Series 11) is “average at best.” Sorry, but it’s true.
But, okay, maybe a new era has arrived. Apple has redesigned its optical heart rate sensor, adding larger LEDs and arranging them closer together in a circular pattern. To back up its claim that the new sensor is the most accurate on the market, the company published a study that was extensive in scope (seven recently released competing devices were tested across various activity types) but limited in usefulness. Each device and workout type was assigned essentially a single score. We don’t see how each device performs in use. The data appears to be selective, and in any case, it doesn’t provide enough information to say whether one sensor is truly better than another, or what exactly it does better. So, I’ll add my own data.
How I Tested the Accuracy of the Apple Watch Heart Rate Sensor
I’m just one person, so my experiments represent a very small, informal study. This is true of any technical reviewer, regardless of their qualifications—so feel free to compare my findings with what others have discovered, but keep these limitations in mind for each of us.
I conducted several tests with an Apple Watch Series 12 and a Garmin Forerunner 570 during workouts. (I wasn’t able to take background measurements outside of workouts.) I wore one device on each wrist, positioned according to the manufacturer’s recommendations, and simultaneously used an electrical chest strap to obtain reference values.
I have relatively fair skin, which may improve accuracy, and I don’t have any tattoos on my wrists, so both sensors should get a clear signal on either wrist. My wrists are six inches, which is slightly smaller than average, so I wore a 42mm watch (both models are available in larger sizes for those who prefer a narrower fit). A good fit is crucial for high accuracy, and I believe I achieved this with both devices. I ensured that both devices fit snugly (but not too tightly) on my wrist.
I tested both devices simultaneously on a treadmill, while running trails, on a rowing machine, and during several strength training sessions. Some of these workouts involved sudden changes in intensity, resulting in peaks and valleys in the graph. Others were more stable. Gripping objects such as dumbbells or the handles of a rowing machine can affect the accuracy of some devices, so I included these workouts in the test as well. Ambient lighting and temperature can also affect accuracy, so I tested in a variety of weather conditions.
Results
In the first phase of testing, the results of which I also published here , the Apple Watch and Garmin performed well, but each had its shortcomings. The Garmin sometimes lagged slightly at the beginning of intervals, but quickly caught up. The Apple Watch didn’t have this problem, but it occasionally missed the maximum values with small jumps in heart rate. In these cases, I would rate the results as equal.
In my other trail runs and on the treadmill, I noticed a similar pattern: both devices were accurate most of the time, but each had its own quirks. Garmin tended to miss the onset of peak activity more often, while the Apple Watch tended to lose data entirely, especially early in the workout.
I once did three mini-workouts at the gym: running on a treadmill, rowing, and strength training. The strength training included several sets of overhead presses, front squats (with a clean grip), and dumbbell curls. Here are the graphs, again with the Apple Watch in red, the chest strap in gray, and this time the Garmin in purple:
Both devices performed equally well on the treadmill, with some hiccups but generally doing a decent job. On the rowing machine, the Garmin fared worse, missing almost half of the second interval. The Apple Watch wasn’t perfect either, overstating the readings in some places and not always recording the lowest value between intervals.
Strength training was unsuccessful for both devices. Garmin often showed underestimated values, while Apple Watch sometimes overestimated them, ultimately producing less data. This image shows this better (each point is marked with a circle):
So is Apple’s sensor really the most accurate wearable?
Based on my data, the biggest news is that Apple is no longer lagging behind in heart rate accuracy. In my tests, the Series 12 is much more accurate than the Series 10 or 11 ever were. Apple has created a very good heart rate sensor, and for that, they deserve a lot of credit. I no longer have to tell people that Apple’s sensor is mediocre.
But does it have the best heart rate sensor? I’m not sure I’m convinced. It’s certainly on par with Garmin’s best sensor, and that’s impressive. On the rare occasions when Garmin struggles, Apple usually shows a more or less accurate value. But I’ve seen near-perfect graphs from Garmin on better days (outside of this test week, though); I’ve never seen anything like that from Apple. The Apple Watch sensor sometimes has trouble setting the right values at the beginning of a workout; it sometimes overestimates readings; it doesn’t reach low values when intervals change quickly; and I’m concerned about the sparseness of the data. It seems like Apple Watch won’t report a value it’s unsure of, which is probably better than recording data that might be incorrect but leaves strange gaps in some graphs.
This forces me to overanalyze the claim of the “most accurate” wearable. If an Apple sensor fails to report data where another device fails, does that make Apple “more accurate” because more of its data points are on the right track? That’s probably a fair claim, but it’s still disconcerting to label this device as “the best.” And if we really want to compare the Apple Watch to all wearables, shouldn’t we also consider chest strap sensors, which are also worn on the body and are objectively more accurate than any optical sensor in a watch?
After all this analysis, I find it hard to definitively call the Apple Watch “the best” for wrist-based heart rate accuracy. But it’s damn good, and I’d put it on par with Garmin. Congratulations, Apple. You’ve managed to match the best sensor on a watch, and I can’t say there’s another one that’s better.