Rings, watches, cuffs and continuous monitors — measured against the lab equipment they claim to replace.
| Story | Evidence | Worth buying | Skip |
|---|---|---|---|
| Your Ring Says 47 Minutes of Deep Sleep. The Lab Says Maybe. | Strong | A tracker is worth it as a bedtime-consistency ledger, because the sleep-versus-wake call is the part that survives comparison with the lab. | Skip paying a premium for sleep-stage detail, and skip any device pitched as a way to find out whether you have a sleep disorder. |
| HRV: The Number Every Wearable Shows and Almost Everyone Misreads | Mixed | Any wearable that measures HRV while you are asleep and still, since that is the condition under which optical sensors match ECG. | Skip percentile ranks against other people, and skip any readiness score built on a single night's reading. |
| Continuous Glucose Monitors Went Over-the-Counter. Here's What They Can and Can't Tell You. | Mixed | One or two sensors' worth of wear, used to test specific meals and post-meal walks against your own baseline. | Skip the open-ended subscription and coaching upsell; the randomised trials that measured weight and BMI found nothing. |
| Your Watch Thinks You Have AFib. Read the Fine Print. | Mixed | A watch with a cleared irregular-rhythm notification plus on-demand single-lead ECG, if you are older or carry a stroke risk factor, because the tracing is the part with value. | Skip buying one to screen an asymptomatic thirty-year-old; the USPSTF calls the evidence insufficient even at 50 and over. |
| The Step Count That Moves Mortality (It Isn't 10,000) | Strong | The cheapest device that reliably reports a weekly average step total, because total daily steps is the only exposure with this much outcome data behind it. | Skip 10,000 as a target, and skip paying extra for cadence or intensity scoring while the cohorts disagree about whether intensity adds anything. |
| Cuffless Blood Pressure Is the Holy Grail of Wearables. It Isn't Here Yet. | Mixed | A validated upper-arm cuff, chosen from the validated-device list first and the price second. | Any cuffless wristband or watch sold as a blood pressure monitor. |
Consumer sleep trackers are good at telling sleep from wake and mediocre at staging it. The validation studies are unusually blunt about which is which.
Heart-rate variability is genuinely linked to mortality. Your overnight RMSSD is still mostly telling you about last night's alcohol.
The sensors are accurate enough. The interpretation — spikes, variability, 'personalised nutrition' — is where the evidence gets thin.
Wrist-worn atrial-fibrillation screening genuinely finds disease. It also generates a lot of notifications that end in nothing.
The dose-response curves from device-measured cohorts bend early and flatten sooner than the marketing suggests.
Home blood pressure is one of the few numbers that changes outcomes. Which is exactly why the device you use has to be a validated one.
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