Sleep Cycle
A weekend of work, and real gaps remain.
A sleep tracker that listens through the phone microphone to detect movement and breathing, then wakes you in a light phase within a chosen window.
A browser cannot do this properly. Know the limits before starting. THE OBSTACLE - Continuous background microphone access is restricted on both mobile platforms - A web app cannot listen all night with the screen off. This is a hard limit, not a workaround WHAT IS STILL POSSIBLE STACK - An installable web app, IndexedDB, a wake lock while charging THE HONEST VERSION - Log bed time and wake time manually, plus a one-tap quality rating - That single pair of numbers, over months, tells you more than most phase detection does THE ALARM - A window rather than a time, with a gentle ramp, works even without phase detection IF YOU HAVE A WEARABLE - Export its data and analyse it yourself. The device already does the sensing Include the manual log, the alarm window and the trend charts.
What you lose
- Phase detection from microphone data, which is a signal-processing problem with years of tuning behind it
- Background audio processing on a phone, which the operating systems restrict heavily
- Long-term trend analysis across millions of nights
If you would rather not build
- A wearable's own data export
- A manual sleep log, which is surprisingly effective
- Sleep as Android, which is open to third-party data
The escape hatch
open source · no votes, no paid placement
FitTrackee
$0Self-hosted activity tracking you can extend with sleep records.
SamR1/FitTrackeefree · open source
Why this verdict
our own opinion · changed only by a person
55/100
Verdict kinda at 55. The sensing is genuinely out of reach in a browser; a manual log with a quality rating covers most of what people learn from these apps.
History
tracked since 10 Aug 2026 · nothing is ever overwritten
Questions about Sleep Cycle
answered from the record above
Is Sleep Cycle free?
No — the plan we track is $3.33 a month. Around $39.99 a year for the premium tier; the figure shown is that divided by twelve.
Can you replace Sleep Cycle by building your own?
ALMOST. A weekend of work, and real gaps remain. Replacement score 55 out of 100, build time a weekend. Read what you lose before you decide.
How much does Sleep Cycle cost?
$3.33 a month on Premium — $39.96 a year. Recorded 10 Aug 2026.
What do you lose by replacing Sleep Cycle?
Phase detection from microphone data, which is a signal-processing problem with years of tuning behind it; Background audio processing on a phone, which the operating systems restrict heavily; Long-term trend analysis across millions of nights. If any of those carry weight for you, keep paying.
Is there an open-source alternative to Sleep Cycle?
Yes: FitTrackee, wger. The prompt on this page is for when you want it your way instead.
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