Your WHOOP band doesn't stop working when the subscription does — the app just goes dark. OpenStrap is what I built so a 4.0 band that would otherwise sit in a drawer keeps doing something: read your own data off it over Bluetooth, keep the raw bytes, and turn them into the numbers you actually look at.
Is it a replacement for WHOOP? No, and I'm not going to pretend it is. They've got years of research and a whole team; this is one person and textbook methods. But it's a real second life for hardware you already own, and your data stays yours.
Tested on WHOOP 4.0 only. Once you start using it, don't reconnect the band to the official WHOOP app — a firmware update could change or break the events this relies on.
- edge — the phone app. Connects to the band, drains it, shows your day. Download the APK →
- backend — the server. Ingests raw frames and computes everything. One Cloudflare Worker; self-host it or use mine.
- analytics — the math. Published methods (Banister TRIMP, Cole-Kripke, and friends) turn heart rate and motion into metrics.
- protocol — the decoders. Raw WHOOP 4.0 record bytes into named fields.
- research — the protocol reference, plus a client to talk to a band yourself.
There are bugs. Please open issues as you find them and I'll work through them. A lot of the protocol — the events especially — is empirical guesswork, and no one person can confirm it to 100%. The more people poke at it, the closer we get to nailing every field down with real confidence.
Not affiliated with, endorsed by, or connected to WHOOP. MIT licensed.