Biohacking Tools & Devices

Consumer tracking hardware measures less than its dashboards imply. Most wrist and ring devices record one or two raw signals - typically optical blood volume and motion - and everything else, sleep stages included, is inferred from those by a proprietary model the manufacturer can change in a firmware update. That is not a reason to avoid them, but it does mean two devices can disagree about the same night without either being broken.

Judge these products on validation and consistency rather than on feature lists. Has the device been compared against a reference standard - polysomnography for sleep, ECG for heart rate variability - and was that comparison published rather than asserted? Does the manufacturer disclose when it changes its algorithm? And treat your own baseline as the only meaningful comparison: night-to-night variance in these metrics is large, so a single reading tells you very little and a fortnight of readings tells you a great deal.