Python client for the $20 Colmi R02 smart ring

Original Article ↗ Hacker News Discussion ↗

Form Factor, Use Cases, and Comparisons

  • Many are attracted to the $20 price and small ring form factor, especially as an alternative to bulky or expensive smartwatches and phone ecosystems.
  • Some want it specifically for sleep tracking without needing to charge a watch overnight. Others plan to augment Apple Watch data with ring data.
  • A common wish: a vibrating alarm in the ring for silent wake-ups. The R02 does not vibrate, which several consider a missed opportunity.

Features, Sensors, and Limitations

  • The ring includes accelerometer, heart rate, blood oxygen, and some “stress” metric; no visible control interface beyond charging LED.
  • Heart rate is sampled every 5–30 minutes in background, with an option for continuous real-time reporting.
  • Battery life reported around four days with high-frequency measurements; many charge it briefly during showers.
  • No built-in temperature sensor; some are seeking a cheap Oura-like ring with temperature but haven’t found one.

Data Quality and Sleep Tracking

  • Several reports say heart rate and step/sleep duration are roughly comparable to more expensive trackers, but SpO2 and “stress” readings are often considered unreliable.
  • Some users find sleep duration significantly overestimated, especially time in bed vs actual sleep. Others feel trends over time are still useful even if absolute values are off.

Open Source, Gadgetbridge, and Hacking

  • Gadgetbridge now has support (in nightly builds) for the R02, enabling phone-free, local data usage.
  • There is interest in custom firmware and using the accelerometer as an input device (gestures, controllers), but raw accelerometer access and mature custom firmware are still limited/unclear.
  • An open SDK exists for the underlying SoC, but toolchain (e.g., Keil) and embedded complexity are barriers.

NFC and Alternative Rings

  • Multiple comments wish for rings with NFC or Java Card for payments, access control, or U2F-style auth; such products exist but are often expensive, clunky, or complex.
  • Some report success with cheap dual-frequency NFC/RFID rings from marketplaces, but capabilities and security vary widely.

Privacy, Security, and Safety

  • The ring will pair with any device that requests it; essentially no meaningful pairing UX or strong authorization. Opinions differ on how problematic this is, given the limited attack surface.
  • Concerns about health-data snooping are raised, but others note similar lax security is common in many BLE devices.
  • Battery explosion risk is mentioned; one commenter believes the tiny, potted battery makes this unlikely, but evidence is anecdotal.

Business Models and Subscriptions

  • Strong criticism of subscription-locked wearables (e.g., expensive smart rings with monthly fees) versus this ultra-cheap, no-subscription device.
  • Some argue devices that require subscriptions are effectively rentals and should be priced or regulated as such.