Fitness bands and smartwatches that monitor your activity are notoriously inaccurate. Wear a bunch of them at the same time and they’ll all return entirely different results. And we’re not talking about slight discrepancies either - the results can differ by several thousand steps.
The idea is the trackers provide you with a general ballpark figure, rather than a precise one, so you can see how your activity varies on a daily basis, and take steps - hah! - to improve on it.
As a result, comparing the results from two or more fitness trackers isn’t usually very helpful - each device will measure activity in its own way, and who is to say what’s right or wrong? However, more advanced wearables - Microsoft Band and Apple Watch, for example - measure your heart rate, and it’s much easier to check how accurate they are. All you need to do is compare the results they produce with the figures from a reliable source.
This is exactly what Rachel Metz did in an article for MIT Technology Review. For several days she wore an Apple Watch and a Microsoft Band while biking to and from work, and then compared the results to those from the Polar H7 Bluetooth chest strap she wore at the same time. A chest strap will always be better at measuring your heart rate than a wrist device, and the Polar H7 is known to be highly accurate. While the results varied from day to day, the Microsoft Band proved to be more reliable. Metz says:
The full story is available to read here.
Tests like the ones performed by Metz aren’t especially scientific, and do highlight the difficultly in accurately measuring vitals (whether it’s heartbeats or footsteps) from your wrist. That said, it seems from her findings that the Band is more accurate than the Watch when it comes to monitoring your heart rate.