Apple says the Apple Watch Series 12 health sensing system is the most accurate heart rate sensor in any wearable, and The Quantified Scientist gave it a first test against a Polar H10 ECG chest strap. Over a day of indoor cycling, running, and weightlifting, the new sensor tracked the strap closely, though not yet better than the Series 11 it replaces.
Indoor cycling was close to perfect, a correlation that rounds to 1.0 and beats 92% of the devices the channel has tested. Running slipped to 0.98, with small misses at higher heart rates early in the run. Weightlifting, the hardest case for wrist sensors, came in at 0.97, better than 85% of devices on the channel's chart, and the old Apple Watch habit of dropping peak readings mostly stayed away. Steps were near exact: across about 5,000 hand-counted steps, the watch was spot-on or slightly high, never more than 14 off per 1,000.
Against the channel's long-term Series 11 data, the correlations look broadly the same, and the Series 11 actually ran a little better; the channel suspects Apple is still tuning its algorithm for the new sensor. GPS was middling on the one test run, cutting corners through bushes. The channel's read is that the sensor's real job is efficient all-day tracking, the five-second readings that 9to5Mac's own review credits with showing how a coffee or a stressful moment moves your heart rate.
Workout accuracy alone isn't a reason to leave a Series 11, on these numbers. The all-day readings might be, and iPhoners waiting for proof get it in the channel's long-term test.
