Methodology
Detecting Sleep With a Phone Instead of a Wearable
A phone on the nightstand cannot see your heart. It can see when you stopped touching it, when you stopped moving, and when the room went dark. Here is how those signals become a sleep record — and where the approach genuinely falls short of a wrist device.
How does phone sleep tracking work without a wearable?
Short answer
MaxDex runs three independent detectors over the night — screen-interaction gaps, operating-system sleep classifications, and accelerometer stillness windows — then selects the best-supported candidate segment and scores it for efficiency and disturbance.
Running three detectors in parallel rather than one is the core design choice. Each fails differently: interaction gaps break if you leave the phone untouched during a long film, classification events are unavailable on some devices, and stillness windows misread a phone left on a desk. Requiring agreement, or picking the best-supported candidate, is more robust than trusting any single signal.
Adjacent fragments separated by less than 90 minutes are merged into one episode, so a 3am bathroom trip does not split a night into two short, low-confidence records.
What does "best effort" mean in the algorithm?
Short answer
Rather than discarding a night that looks imperfect, the engine keeps the episode and scores it — efficiency, movement index, disturbance score, and estimated awake minutes — so an interrupted night is recorded as an interrupted night instead of vanishing.
This is the opposite of the common approach, which is to throw away readings below a confidence threshold. Discarding produces a tidier chart and a worse model: the nights most worth knowing about are exactly the broken ones, and a gap in the record reads to the sleep-debt calculation as though the night never happened.
Each episode carries a classification derived from its confidence and disturbance scores, so the planner and the AI can treat a fragmented six hours differently from a clean six hours.
Related
How does MaxDex handle an uncertain night?
Short answer
A duration-confidence weight blends the reading toward your personal sleep need. Effective hours = confidence × measured hours + (1 − confidence) × your sleep need, so a barely-detected night regresses toward "probably normal for you" rather than swinging the score.
Without this, a single noisy detection would crater a sleep score and a week of debt figures. With it, the model says the honest thing: we are not sure what happened, so we will not pretend to be.
Manually entered sleep carries no confidence value and is trusted at face value. The same duration-confidence function is shared by the Android detector and the iOS Apple Health path, so a short or fragmented night degrades identically on either platform rather than one being quietly more optimistic.
Does it work for shift workers and day sleepers?
Short answer
Yes. Time of day is explicitly not a gate on what counts as sleep. A main sleep episode starting at 9am is treated as a first-class night, not discarded as an anomalously timed nap.
Most consumer sleep tracking bakes in an assumption that sleep happens at night, then behaves strangely for the roughly one in five workers whose schedules do not. Typical sleep timing is used as a weak prior when disambiguating between candidate segments — never as a filter that rejects them.
Naps are detected separately, with a lower minimum duration, and contribute a bounded pressure relief rather than overwriting the main sleep record for the day.
How accurate is phone-based sleep tracking really?
Short answer
Phone detection infers sleep duration and timing from on-device behaviour and stillness without requiring a wearable. It is designed for daily energy planning rather than clinical sleep staging.
The framing is that this is a practical estimate of when you slept and your rest patterns, built for planning your day rather than medical diagnostics. If you need sleep-stage data or clinical-grade measurement, a dedicated medical sleep study is the right tool.
Reviews of consumer sleep technology have found that wrist devices perform well on total sleep duration while varying on stage classification. What a phone genuinely offers is convenience: it is already on your nightstand, charged every night, providing consistent daily trend tracking for your planner.
Sources
- de Zambotti, Cellini, Goldstone, Colrain & Baker (2019). Wearable Sleep Technology in Clinical and Research Settings. — Medicine & Science in Sports & Exercise
How is the sleep score itself computed?
Short answer
score = (effective hours ÷ your sleep need × 100) − debt penalty + consistency bonus − oversleep penalty, clamped to 0-100. The debt penalty caps at 30 points, the consistency term is (consistency − 0.6) × 20, and oversleep beyond 1.5 hours over need costs up to 12.
The oversleep penalty is the part people query, so it is worth stating the reasoning: the relationship between sleep duration and metabolic and mortality outcomes is an inverted U, not a straight line. Large meta-analyses have found elevated risk at both short and long durations. The penalty is kept deliberately gentle — capped at 12 points and only engaging beyond 1.5 hours over your need — so one genuinely restorative long night is not punished.
Frequently asked questions
Is a phone as accurate as an Oura ring or Whoop for sleep?
Does the phone need to be on the bed or under the pillow?
Does sleep tracking drain my battery?
What happens if I forget my phone or it dies overnight?
3 more questions
How does MaxDex handle naps?
Does it track sleep stages like REM and deep sleep?
Is my sleep data uploaded anywhere?
Last reviewed August 28, 2026 by the MaxDex Services team. How we research and review this.