An app that makes a WHOOP 4.0 useful without a WHOOP subscription. Connects to the band over Bluetooth, computes everything on your phone locally iOS and Android.
Not affiliated with WHOOP. Not a clone of their app or their scores — see below.
"The goal of the so-called OpenStrap project is not to re-create the WHOOP app. Rather, the algorithms and processing methods are developed from scratch, based on public research… The health data collected from the watch never leaves the phone."
"When a membership lapses, the hardware is basically useless. You own it, you still can't use it — it just goes dark, because the app stops talking to it. So you've got a perfectly good sensor turning into a paperweight."
| iOS | Join the TestFlight beta → — normal TestFlight install, no sideloading, no computer needed. |
| Android | Download the APK → — allow installs from unknown sources and open it. |
Quit the official WHOOP app before you pair. Bluetooth only lets one app own the band at a time.
Prefer to sideload the unsigned IPA instead of using TestFlight? That still
works — see guides/IOS_SIDELOAD.md.
No subscription, no paywall, no company behind this.
If OpenStrap gave your band a second life, a small tip genuinely helps.
Bitcoin
bc1qvtcch38dcwp967ar764uu6eetw7tf907844wfq
EVM — Ethereum · Base · Arbitrum · Optimism · Polygon
0x8310C89393366b7eBCD47ABa82e1dfB5ECeFFbD9
What donations actually pay for →
Nothing is gated behind paying, and nothing ever will be.
Bug reports from real bands are worth more than money — there's only one
person's physiology in the test data otherwise.
My subscription lapsed and a perfectly good sensor turned into a bracelet. The hardware never stopped working, only the app that made it useful did. So I reverse-engineered enough of the band's Bluetooth protocol to talk to it myself, wrote the analytics from scratch off published research instead of guessing at WHOOP's formulas, and built an app around the result. Now it works without them, and anyone else stuck with the same drawer-bracelet problem can use it, or go dig through the code themselves.
- WHOOP 4.0 only. Haven't touched a WHOOP 5, don't know if it even shares a protocol.
- Not affiliated with WHOOP, doesn't talk to their servers.
- Not a clone of their algorithms — different math, published methods, cited in the analytics repo. Don't expect identical numbers to what their app shows.
- There are bugs. Some I know about, more I probably don't. Open an issue if something looks wrong.
- Don't bounce between this and the official WHOOP app. A firmware push from their app could change the records this one depends on, and there's no fixing that from here. Pick one and stay on it.
 Today |  Sleep |  Heart |
 Stress |  Breathing |  Body |
 Steps |  Workouts |  Records |
 Recap |  Profile |
iOS also gets a home-screen widget, a lock-screen/Dynamic Island Live Activity, and a couple of Siri shortcuts.
 Widget |  Battery widget |  Live Activity |
Every screenshot above is real output from a WHOOP 4.0.
Health — heart rate, HRV, sleep staging, recovery/readiness, strain, stress, an HRV spot-check, real-time breathing coherence.
Activity — auto-detected workouts, live workout tracking with GPS routes, heart-rate zones.
Your data, elsewhere — writes to Apple Health (HealthKit) and Google Health Connect: sleep stages, resting HR, HRV, respiratory rate, active energy and workouts. Only things the band actually measures — never the derived scores, which have no native type and would be fabricated. Exports are idempotent, so a day re-deriving never duplicates samples. You can also export the entire local SQLite database to a file whenever you like — it's your data, in a format anything can open.
Background sync — the band drains without you opening the app. Android runs a foreground service with a 15-minute watchdog worker and re-attaches via CompanionDeviceManager. iOS uses a background processing task plus a light refresh task, and a separate restore Bluetooth central that relaunches the app when the band reconnects.
Everything else — trends/history, a journal with on-device correlation insights ("what actually moves your numbers"), cycle tracking, a deterministic coach, a shareable weekly recap, a BYOK AI assistant, home-screen widgets, iOS Live Activities, Siri shortcuts, a smart alarm that buzzes the band.
- iOS background sync is best-effort. It genuinely works (see above), but Apple doesn't give third-party apps a real background-service option, so the OS decides when those tasks actually run. Syncing while you haven't opened the app in a while is "usually," not "always." Android has no such limit.
- Metrics are approximations off published research — not medical-grade, not validated against a lab, don't treat any of it as a diagnosis.
- Not on the App Store or Play Store yet. iOS is a public TestFlight beta, which is a normal install but still a beta; Android is an APK straight off Releases.
- WHOOP 5.0 / MG support is in progress and experimental — the band is detected and spoken to, but it hasn't been validated against real 5.0 hardware. WHOOP 4.0 is the only one that's actually tested.
git clone https://github.com/OpenStrap/edge.git
cd edge
cp .env.example .env
flutter pub get
flutter run --dart-define-from-file=.envQuit the official WHOOP app before you pair — Bluetooth only lets one app own the band at
a time. iOS signing and the App Group setup for the widget/Live Activity is its own
longer story — see guides/IOS_INSTALLATION.md.
WHOOP band → Bluetooth → protocol decoder → local storage → analytics → the UI
openstrap_protocolturns bytes off the band into records.openstrap_analyticsturns those records into metrics, each with its own confidence score attached — nothing gets faked when the data isn't there.- this repo is the glue: Bluetooth reliability, local storage (versioned, so an algorithm update never silently overwrites old results), background sync, the UI.
- everything that matters stays on the phone.
The band doesn't have a normal documented API — it's a proprietary protocol, and getting it to behave reliably took a while. Short version: the clock ships unset (skip setting it and every timestamp comes out garbage), history comes off in batches that need an exact 8-byte token echoed back or the band just re-sends the same data forever, and the local save has to happen before that acknowledgement goes out, not after, so a crash mid-sync can't lose anything.
The full blow-by-blow lives in the protocol repo's README — genuinely the more interesting read if you're into this kind of thing.
Everything's computed and stored locally. No cloud account required, no backend this needs to work day to day. Your health data never leaves the device unless you explicitly send it somewhere.
Being precise about the network, since "no cloud" gets said too loosely. Nothing below is required for the app to work, and none of it carries health data except the two you turn on yourself:
- Anonymous diagnostics (Firebase crash/performance). On by default in GitHub release builds — switch it off in your profile and collection stops immediately. Not present at all in App Store / Play Store builds. Never includes health data.
- OTA/announcement pointer — checks whether there's a newer build.
- Legacy account import — one-time, only if you had an old OpenStrap cloud account.
- BYOK AI assistant — only if you configure a provider. Your key, your account. Be aware that the prompts contain your health data: to answer "why is my recovery low", the assistant is given your metrics to read. That data goes to whichever provider you chose, under their policies, not ours.
- Health-data contribution — opt-in, off by default, GitHub builds only. Uploads your local database wholesale, which is the entire point of it. It's the only thing here that sends the whole database rather than a slice.
Full detail in PRIVACY.md.
lib/ble/ Bluetooth + sync
lib/data/ local storage + the repository seam the UI reads from
lib/compute/ runs the analytics pipeline, writes results
lib/state/ AppState, the one source of truth
lib/ui/ every screen
Protocol decoding and analytics live in their own repos — protocol, analytics.
Found something broken? Open an issue. Found something broken and fixed it? Even better, send the PR. Protocol-level stuff (new record types, opcodes) belongs in the protocol repo, metric/formula changes belong in analytics, anything about the app itself — Bluetooth, storage, UI — belongs here.
CONTRIBUTING.md has the details: which repo a change belongs in, how to run the three packages together locally, and the two rules that matter most — never fabricate a number when the data isn't there, and cite the published method you're implementing.
Security problems shouldn't go in a public issue — see SECURITY.md for private reporting.
Every one of these people made the app better — mostly by using it on a real wrist and reporting what came out wrong.
The most useful contribution isn't necessarily code. There's one person's
physiology in the test data, so a bug report from a different body on a
different band is worth a great deal — see
CONTRIBUTING.md.
That cliff in mid-July is Hackaday and Adafruit covering it on the same day.
Free, MIT, no company behind it. If it gave your band a second life, DONATE.md has the BTC and EVM addresses and explains what they actually pay for. Bug reports from real bands are worth more than money, though.