The pitch for sleep wearables is that sleep is invisible, so you need a sensor strapped to your body to see it. Half of that is true. The other half is that the single most useful fact about last night - how long you slept and when - is sitting in your phone already, no extra hardware required.

What a wearable measures vs what a phone can infer

A ring or a strap sits against your skin all night and reads your body directly: heart rate every few seconds, heart-rate variability, skin temperature, and movement. From those continuous signals it models your sleep stages and reaches a recovery number. A phone has none of that contact. What it does have is motion - the accelerometer that knows when the device, and by proxy you, went still for the night and stirred in the morning. From that quiet window it can infer when you fell asleep, when you woke, and the duration in between, and write that to Apple Health like any other sleep source.

What the phone gets right, and where wearables still win

The phone is good at the two things that matter most: duration and timing. For the large majority of nights, knowing you were down for roughly seven hours starting near midnight is most of the signal you will ever act on. Stages are where the phone has to estimate rather than measure, and it should say so.

Where the wearables still earn their price is the body itself. Continuous heart rate, HRV and the staging that builds on them need skin contact a phone cannot fake. If you specifically want HRV trends, a true deep-versus-REM breakdown, or athlete-grade recovery, that is the wearable’s real edge and worth paying for.

Metric	Phone-only	Ring / strap
Duration	Good - inferred from motion	Good - sensor confirmed
Timing (sleep and wake)	Good - when you went down and got up	Good
Stages (light / deep / REM)	Estimate only	Better - from HR and movement
HRV and continuous HR	Not measured	Yes - the real wearable edge
Cost	Phone you already own	Ring or strap, often a subscription
Privacy	On-device, no account	Usually synced to a cloud

Phone stage detection is an estimate, not a clinical reading. Wearable capabilities vary by brand and tier; check each maker’s site for specifics.

Why a good-enough number still drives a daily score

You do not need clinical staging to act well. The decisions sleep actually informs - whether to go hard or go easy today, whether last night was short, whether your bedtime is drifting later all week - turn almost entirely on duration and timing, both of which a phone reads well. Stages add colour; duration carries the weight.

Duration45%

Timing & consistency30%

Estimated depth15%

Continuity10%

Illustrative weighting of what a practical sleep number leans on. Duration and timing - the parts a phone reads well - do most of the work; staging is the smaller refinement.

That is why a phone-derived sleep figure is enough to feed a real daily score. In Soren, auto-detected sleep is one of three pillars folded into a single 0-100 Soren Score, alongside focus and HealthKit movement, all computed on the iPhone.

A Soren Score sleep, focus and movement in one number, no watch

An illustrative score. Sleep here comes from iPhone motion written to Apple Health, not a wearable - good enough to move the number.

The quiet upside: it never leaves the phone

There is a privacy dividend to doing this on-device. A wearable’s nightly read is usually only fully legible through the maker’s app and their cloud, behind an account and often a subscription. A phone-only approach can keep your sleep where it was recorded. Soren has no account and no servers: sleep is detected on the iPhone, written to Apple Health, scored locally, and nothing is shipped off the device.

So do you need a wearable?

Want HRV, athlete-grade recovery or a true stage breakdown → a ring or strap still wins.
Mostly want to know how long and how consistently you slept → your phone already does that.
Want a private daily score that counts sleep without a watch → Soren.

One caveat: Soren is iOS 17+, on the App Store, and its sleep staging is an estimate, not a medical reading. If what you want is the big, actionable facts about your sleep without strapping anything on, the phone in your pocket is most of the way there already.

Get Soren →

Sleep figures and the weighting above are illustrative, not measured. Soren detects sleep from iPhone motion and labels stages as estimates; it is not a medical device and does not diagnose anything. Tell us if we have something wrong at hello@sorenlabs.xyz.