OpenStrap is a screenless 24/7 sensor pill on a band — continuous heart rate, HRV, SpO2, skin temp and motion, streamed over an open BLE protocol to whatever you build. Open schematics. Open firmware. Open SDK. No cloud. No account. No subscription. Ever.
We reverse-engineered the leading subscription strap down to the byte — its BLE protocol, its frame layouts, its sensors. Then we built reference algorithms and validated them against that real hardware, night after night. OpenStrap is what we'd ship if the incentive were you owning the device — because it is.
Morning readiness from overnight HRV, resting HR and sleep debt.
logistic HRV modelCardio load through the day, anchored to your wake cycle — no idle drip.
TRIMP, HR-reserveOnset, stages, disturbances and final wake from motion + heart signals.
Cole–Kripke actigraphyIntraday stress in 2-minute windows from beat-to-beat variability.
Baevsky indexContinuous optical heart rate with beat-to-beat RR intervals.
green PPG, 24/7Blood-oxygen sampling during sleep via red + infrared optics.
r/ir ratio-of-ratios±0.09 °C clinical-grade skin temperature, trends and deviations.
AS6221 sensorOvernight breathing rate derived from respiratory sinus arrhythmia.
RSA spectralThe pill streams the raw signals; the SDK ships reference algorithms for every derived metric, each with a published audit document — references, method, research-backed verdict. Use ours, or write better ones.
Two boards, like the incumbents ship: a digital main board and a sensor flex pressed against the skin window with discrete optics — green for heart rate in motion, red + infrared for SpO2. Sealed pill, wireless charging through the lid, no exposed contacts, no ports.
No wearable company shows you this. We will, because the point is that you own the thing: every part, every price. This is the live engineering BOM at small-batch pricing — it falls hard at volume, and pre-sale pricing passes that on.
| Part | Function | qty-10 |
|---|---|---|
| nRF52840 module | MCU + Bluetooth LE | $6.00 |
| AFE4404 | optical front-end | $2.40 |
| g / r / ir LEDs + photodiode | PPG · SpO2 optics | $2.40 |
| BMI270 | 6-axis motion | $2.80 |
| AS6221 | skin temperature | $2.00 |
| nPM1300 | power + fuel gauge | $2.20 |
| W25Q128 | 16 MB flash | $1.40 |
| W25N01 NAND | 128 MB raw buffer | $1.20 |
| DRV2605L + LRA | haptics | $2.40 |
| BQ51003 + coil | Qi wireless charging | $2.20 |
| LiPo 300 mAh + PCM | battery | $4.00 |
| passives · TVS · LED | ~35 small parts | $4.00 |
| Total | ≈ $33 |
~$32 of parts at ten units — falling toward ~$13 at production volume. Now you know roughly what your $720-over-three-years strap costs to build. The difference is the business model, and the business model is the product. Schematics, gerbers and firmware publish with batch 001.
Open-licensed schematics, layout and enclosure for the sensor pill + band. Build one, mod one, repair one. The battery is replaceable and the firmware is unlocked — your warranty is the repo.
Open Zephyr-based firmware on the nRF52840 — every sensor exposed, on-pill flash buffering, OTA updates. Flash ours, fork it, or write your own from the hardware docs.
A documented BLE protocol and client libraries for streaming raw signals and synced history into whatever you build — plus audited reference algorithms for recovery, strain, sleep and stress. The pill never phones home.
Slide-on wireless battery pack that charges the pill while you wear it. Same sealed Qi path, zero downtime.
The sensor-flex architecture has a designed-in path to ECG electrodes on a future flex revision.
Different band, different sensor mix, different algorithms — the whole point of open hardware is that we don't get to decide where it ends.
The incumbent strap reverse-engineered to the byte. Our analytics engine — recovery, strain, sleep, stress — running on real nightly data and regression-tested against it.
Two-board pod, discrete optics on a sensor flex, Qi charging, full BOM costed. Specs and interface docs written for contract engineering.
Electrical design and first assembled prototypes. Bring-up gated on on-wrist optical signal quality, scored against ground-truth data from the strap we cracked.
Small sealed-pod run for the people on this list. Schematics and firmware publish the same day the hardware ships.
Join the founder list for batch 001. No charge today, no spam — one email when pre-orders open, $150 pre-order pricing locked for the list ($249 at retail).
Pre-order $150 · retail $249 · $0/month forever
▸ You're on the list. Welcome to batch 001.
The hard half already exists and runs every day: the BLE protocol work, the decoders, and reference algorithms (recovery, strain, sleep, stress) validated nightly against a real commercial strap we reverse-engineered, with a regression harness over real captured data. The hardware is specced to the part number with engineering underway — and we publish the BOM above precisely so you can judge it. We won't take a dollar until boards exist.
You pay for hardware once; margin on hardware funds the project. There's no cloud to pay for — the pill talks straight to your devices — so there are no server costs to recover. That's the structural trick the subscription model hides. No catch: if we disappear, your strap keeps working and the repos stay forked.
On the pill — 16 MB of flash buffers weeks of data — until you sync it over BLE to a device you control. From there it's wherever you decide: the protocol and SDK are open, and nothing ever phones home.
Our acceptance gate is head-to-head: prototype on one wrist, the leading commercial strap on the other, nightly metrics compared over weeks. Every algorithm ships with an audit doc citing the research it implements. We'll publish the comparison data with batch 001 — wins and misses both.
Hardware under an open hardware license (CERN-OHL family), firmware and apps under a copyleft software license. Final exact licenses announced before pre-orders charge — the commitment that matters: you can build, modify and repair without asking us.
Honestly: prototype boards in late 2026, founder batch after validation passes — we'd rather slip than ship a strap with bad optics. Joining the list costs nothing and reservations are refundable until your unit ships.