Apple Watch Series 6 vs. Fitbit Sense: The Blood-Oxygen Watch Wars
Apple's SpO2-equipped Watch Series 6 and Fitbit's stress-sensing Sense are fighting for the same wrist, with very different priorities.
The wearables market just got a lot more interesting. Apple shipped the Watch Series 6 last month, and its headline feature is a blood-oxygen (SpO2) sensor built right into the back of the case — you press your wrist to the display, wait fifteen seconds, and get a percentage reading of how saturated your blood is with oxygen. It starts at $399, and Apple paired the launch with a new budget option, the Watch SE, for people who want the ecosystem without the flagship price.
Fitbit didn’t wait around. Its answer is the Sense, at $329, and instead of chasing Apple’s SpO2 feature spec-for-spec, it leans into something different: an EDA sensor that measures electrodermal activity — essentially skin conductance — to flag signs of stress. Put your palm over the watch face for a couple of minutes and it tries to tell you whether your body is tensing up, before you’ve consciously noticed.
That’s the real split here. Apple is betting on a respiratory/cardiovascular story — SpO2 sits alongside its existing ECG feature as part of a broader “understand your heart and lungs” pitch, which makes obvious sense in a year when a respiratory virus is on everyone’s mind. Fitbit is betting on mental health and stress management as the differentiator, wrapping the EDA sensor into its existing sleep-tracking strengths.
Where they actually overlap
Both watches track ECG, both track sleep, both count steps and workouts. If you strip away the marketing, the core fitness-tracking experience is going to look pretty similar day to day. The differences show up at the edges.
Battery life is the most practical one. Fitbit is claiming around six days on a charge for the Sense. Apple Watch Series 6 is still in the roughly-18-hours camp, which means nightly charging is non-negotiable if you also want it to track your sleep — you’re squeezing that charge into a shower or breakfast window. If battery anxiety is a dealbreaker for you, that gap alone might decide this.
Platform lock-in is the other big one. The Apple Watch, as always, only works with an iPhone. The Fitbit Sense works with both iOS and Android, which matters enormously if you’re not already bought into Apple’s ecosystem or you switch phones across brands.
So which one should you get?
Neither company has published rigorous validation data proving these new sensors are clinically reliable for the general public, and I’d treat both SpO2 and EDA readings right now as “interesting personal data point” rather than “diagnostic tool.” That said, if you’re already carrying an iPhone, the Series 6 is the more complete smartwatch — better app ecosystem, tighter integration, the works. If you’re on Android, want longer battery life, or care more about stress tracking than blood oxygen, the Sense is a serious, cheaper alternative.
What’s notable is that this is the first time in a while Fitbit has shown up with a feature Apple doesn’t have at all, rather than just cheaper hardware. Worth watching whether Apple answers with its own stress-tracking play down the line.