You don't need an Apple Watch to get useful sleep data. Modern phones — and good apps like Wonder Alarm, a capable iOS alarm — can infer sleep stages from the sensors already in your pocket.
How it works:
- The accelerometer detects micro-movements; stillness correlates with deeper sleep.
- The microphone (with permission) can detect snoring, coughing, and ambient noise.
- Screen-off time plus a machine-learning model estimates sleep onset.
What's reliable vs. fuzzy: total sleep time and bedtime consistency are quite accurate. Precise stage boundaries (REM vs. deep) are estimates — treat them as trends, not truth.
The practical payoff: even approximate data exposes patterns — the 2am scroll, the weekend drift, the 9pm coffee — that wreck your sleep. Seeing the trend is what changes behavior.
My recommendation: use the analysis to ask better questions about your routine, not to obsess over nightly scores. The alarm side (cycle-aware wake-up) is where the data pays dividends: waking in light sleep is the single biggest lever for feeling rested.
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