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Jring / 56ff

PulseLoop support: ✅ Supported & tested

The cheapest ring PulseLoop drives — a $7–12 commodity device built by the keeprapid OEM and white-labeled under many brands. It speaks a custom 56ff BLE protocol and is the only PulseLoop-supported ring that reports blood pressure and (profile-derived) blood sugar.

Set the ring up in the official Jring app first

Pair and initialize the ring once with the original Jring / KeepFit app before connecting it to PulseLoop. First-time setup sends some device initialization commands that we haven't fully reverse-engineered yet; without that one-time setup a fresh ring may not stream all data correctly to PulseLoop. After it's been set up once, PulseLoop can connect to it directly.

At a glance

Detail
SoC Renesas DA14531 (ARM Cortex-M0)
Bluetooth BLE 5.x
PPG sensor Unknown (HR/SpO₂, no skin temperature)
Accelerometer Yes
Battery / life Unknown
Waterproof Varies by seller
Price $7–12
Protocol Custom 56ff (SXR KeepFit SDK), fixed 20-byte frames, cleartext
App Jring / KeepFit
Custom firmware ✅ Renesas SUOTA (SR08 reference)

Manufacturer

  • keeprapid.com (ShenXinRui / 深新锐) — Chinese OEM
  • White-labels under brands: Jring, KeepFit, JYouPro, RWfit, Tag
  • SDK: SXR KeepFit SDK (com.sxr.sdk.ble.keepfit)

Hardware

Component Detail
SoC Renesas DA14531 (Dialog DA145XX family)
SoC architecture ARM Cortex-M0
PPG sensor Unknown (PPG HR/SpO₂, no skin temperature)
Accelerometer Yes (steps, sleep stages, activity)
Memory Unknown
Weight Unknown
Waterproof Unknown (varies by seller)

Protocol

The 56ff protocol was reverse-engineered from scratch — see the full writeup for the BLE teardown and how the packet formats were decoded.

Property Value
Service UUID 000056ff-0000-1000-8000-00805f9b34fb
Write characteristic 000033f3-...
Notify characteristic 000033f4-...
Additional chars 0x33F5, 0x33F6 (purpose unknown)
Secondary service 0x57FF
SUOTA service 0000fef5-... (firmware OTA)
Frame size Fixed 20 bytes
Encryption None (cleartext)
Standard BLE services DIS (0x180A), Heart Rate Service (0x180D)

Capabilities

Capability Status Notes
Heart rate — spot / live / history ✅ BPM
SpO₂ — spot / history ✅
Steps / distance / calories ✅
Sleep (light / deep / awake) ✅ No REM
Blood pressure ✅ Direct sensor reading via 0x23/0x24, no user profile required
Blood sugar ✅ Profile-derived estimate (not a real glucometer) — requires user profile
Stress ✅ 0–100
Fatigue ✅ 0–100
HRV ✅ ms
Battery level ✅
Find device ✅
REM sleep ❌
Skin temperature ❌ No sensor — official app shows 0°C/32°F placeholder
Continuous background sync ❌ Command-response only, ~20s idle timeout

Blood sugar requires a user profile

Blood sugar is a profile-derived estimate from sex/age/height/weight (sent via 0x02 CMD_SET_USER_INFO), not a real glucometer reading — changing the profile changes the value.

What the 56ff ring CANNOT do

  • REM sleep detection
  • Body temperature (no skin temperature sensor)
  • Continuous streaming (command-response only, ~20s idle timeout)

Known models

  • SR08 — open-source reference hardware (atc1441/ATC_SR08_Ring)
  • Generic "SMART_RING" — sold on AliExpress for $7–12

Firmware

  • Version format: 003A002AV138 — an 8-hex family code (003A002A) + V + version number. The family code identifies the specific hardware variant.
  • Update manifest: http://download.keeprapid.com/apps/smartband/keepfit/fwupdater/{en|zh}/{family}/update.json — returns the latest version, the binary URL, and its MD5.
  • Binary: http://download.keeprapid.com/apps/smartband/keepfit/fwrelease/{family}/V{n}.bin — a Renesas/Dialog SUOTA image.
  • Flashing: Renesas SUOTA (0xFEF5 service) to the DA14531.
  • All firmware traffic is plain HTTP with no token or signature — integrity is an MD5 only.

Background behavior

  • Idle timeout: ~20 seconds of inactivity
  • Keepalive: 0x3A ping/pong
  • Binding: 0x4B custom protocol (NOT OS createBond())
  • Official app runs periodic background sync

Hackability

🥈 Protocol-Documented

  • ✅ Protocol fully reverse-engineered (writeup; also the iOS repo's docs/ring-protocol.md)
  • ✅ Open-source firmware skeleton: atc1441/ATC_SR08_Ring
  • ✅ Official SDK protocol doc: 深新锐蓝牙协议v3.0.docx (keeprapid/krwatch)
  • ✅ Cleartext BLE, no encryption
  • ✅ Renesas SUOTA for firmware OTA
  • Price: $7–12

See the hardware overview for the full cross-manufacturer comparison tables, or the Colmi / Yawell family for the more sensor-rich option.