Phase 1 specifies the JSON envelopes that every WIA-MED-020 conformant device, mobile app, hub, dashboard, or EHR bridge MUST be able to read and emit. The envelopes are designed to round-trip byte-identically through encode and decode so that signed payloads survive intermediate processing. JSON Schema 2020-12 documents are the source of truth, served from https://wiastandards.com/wearable-health/schemas/.
The device record is the registration envelope. It binds a device identifier to a patient, declares the device manufacturer / model / firmware, lists supported measurement types, and (for clinical-grade devices) carries the regulatory-clearance reference plus the calibration chain pointer.
{
"wia_wearable_health_version": "1.0.0",
"type": "device",
"device_id": "did:wia:device:apple-watch-S9-01HXY",
"patient_id": "did:wia:patient:01HXY",
"manufacturer": "Apple",
"model": "Watch Series 9",
"firmware_version": "watchOS 11.2",
"registered_at": "2026-04-27T10:00:00Z",
"clinical_grade": false,
"supported_measurements": ["heart_rate", "ecg", "spo2", "step_count", "sleep_stage"],
"signature": { "alg": "Ed25519", "value": "AY3o..." }
}
One measurement is one observation. Required fields: measurement_type, device_id, patient_id, captured_at, value, unit, signature. Reserved measurement types include heart_rate, step_count, distance, calories, sleep_stage, spo2, ecg, glucose, sbp, dbp, temp, weight.
A session bundles many measurements over a contiguous activity, sleep, workout, monitoring, fasting, or recovery period. The session carries a summary block whose shape varies per session kind — a sleep session summarises REM / deep / light / awake minutes, an activity session summarises distance and calories.
An alert is a clinically meaningful event derived from measurements. The severity ladder is info, warning, urgent, critical; critical alerts MUST be pushed within 60 seconds of detection per the patient consent envelope. The alert carries an evidence_measurement_ids array linking to the underlying measurements that triggered the rule.
Clinical-grade devices MUST publish a calibration record at least monthly. The record ties the device to a national metrology institute reference (NIST, PTB, KRISS, NMIJ, NIM), records the as-found and as-left uncertainty, and chains to the previous calibration record. This creates an unbroken audit trail back to a national standard.
/min, mg/dL, mm[Hg], etc.).did:wia:patient:...).This chapter participates in the WIA-MED-020 8-chapter survey. Each chapter is intended to be readable standalone, but together they map the full surface of the standard. The Phase numbering used throughout (Phase 1 / 2 / 3 / 4) refers to the four-document specification — Chapter 4 covers Phase 1, Chapter 5 covers Phase 2, Chapter 6 covers Phase 3, Chapter 7 covers Phase 4.
https://github.com/WIA-Official/wia-wearable-health-conformance is the single source of truth. When this book and the test suite disagree, the test suite wins.wia/wearable-health-host:1.0.0 implements every Phase 2 endpoint with mock data; integrators exercise their bridge against it before going to production.cli/wearable-health.sh ships sample envelope generators (validate, device, measurement, alert, consent, info subcommands) so an implementer can produce conformant payloads without hand-rolling JSON.Every choice in this standard is filtered through the question: "does this make wearable data more useful for the patient and their care team, or just easier for vendors to ship?" When the two conflict, the patient and care team win. That is why the standard mandates explicit patient consent for cross-host data flow, refuses to accept clinical-grade claims without regulatory clearance, and requires implementations to surface calibration provenance so that clinicians can verify the source quality of every measurement they make decisions on.