OpenStrap Edge — use your WHOOP 4.0 without a subscription
Your WHOOP 4.0 doesn’t stop working when the subscription does.
Only the app goes dark. Edge pairs with the band over Bluetooth, decodes what it<br>recorded, and works out your sleep, recovery, strain and the rest —<br>entirely on your phone. No account, no subscription, and no server that ever<br>receives your health data.
Get it on iOS<br>TestFlight beta
Get it on Android<br>APK from Releases
Free and MIT licensed. Not affiliated with WHOOP.<br>Tested on WHOOP 4.0 — 5.0 / MG support is experimental.
Today
Sleep
Heart
Recap
Every screenshot is real output from a WHOOP 4.0.
It runs on your phone
The band talks to the app, the app decodes the bytes and computes every metric<br>locally, and the results are stored on the device. There’s no server that<br>sees your health data — that isn’t a setting, it’s the<br>architecture.
Precisely, because “no cloud” gets said too loosely: GitHub Release<br>builds send anonymous crash diagnostics by default (switchable off); store<br>builds send none. Neither ever includes health data.<br>Detail →
Published methods, cited
Banister TRIMP, Cole–Kripke, Lomb–Scargle, van Hees and friends.<br>Nothing invented, no neural net guessing at WHOOP’s formulas. You can go<br>read the paper and decide whether you trust the number.
It admits what it doesn’t know
Every metric carries a confidence and a tier. When the data isn’t there<br>you get a dash, not a plausible-looking guess. SpO2 and skin<br>temperature are relative-only, because that’s what the band actually<br>gives up.
Not a WHOOP clone
Different algorithms, different numbers. They have years of research and a<br>team; this is textbook methods over a reverse-engineered byte stream. It trends<br>correctly and it’ll tell you when you’re under-recovered. It<br>isn’t their secret sauce and never claims to be.
Before you install
Quit the official WHOOP app before pairing. Bluetooth only lets one app own the band at a time.
Pick one and stay on it. A firmware push from the official app could change the records this depends on, and there’s no fixing that from here.
Not medical-grade. These are approximations from published research, not validated against a lab. Nothing here is a diagnosis.
There are bugs. It’s a beta built by one person. Open an issue when something looks wrong — that’s genuinely the most useful thing you can do.
How it’s put together
band → Bluetooth → protocol decoder → local storage → analytics → the UI
edge<br>The app. Bluetooth, storage, the compute pipeline, every screen.
protocol<br>The decoders. Raw band bytes into named fields. Pure Dart, zero dependencies.
analytics<br>The math. Published, peer-reviewed methods with citations in the code.
research<br>The lab notebook. The protocol written down, plus a Python client.
Where it’s got to
The cliff in mid-July is Hackaday and Adafruit covering it on the same day.<br>Chart generated from the GitHub API and served from this site, rather than<br>embedded from star-history.com or starchart.cc — there is no analytics or<br>third-party service on this page. (The screenshots above load from GitHub, which<br>also hosts it.)
☕ Like it? Help keep it going.
No subscription, no paywall, no company behind this. If OpenStrap gave your<br>band a second life, a small tip genuinely helps.
Bitcoin<br>bc1qvtcch38dcwp967ar764uu6eetw7tf907844wfq<br>EVM — Ethereum · Base · Arbitrum · Optimism · Polygon<br>0x8310C89393366b7eBCD47ABa82e1dfB5ECeFFbD9
Tap an address to select it. What this actually pays for: the Apple Developer<br>membership that keeps the TestFlight build alive, a second band to get<br>WHOOP 5 support tested, and coffee.<br>More →
Nothing is gated behind paying, and nothing ever will be.<br>Bug reports from real bands are worth more than money — there’s only<br>one person’s physiology in the test data otherwise.