Smart Rings vs. Watches as a Cryonics Death-Alarm

Published October 26, 2025 · by Trent Tompkins

Here is an unglamorous truth about cryonics that never makes the brochures: your outcome depends enormously on how fast preservation begins after you are pronounced. The brain starts to degrade from oxygen starvation within minutes, and every hour a standby team is late is damage no future technology is guaranteed to undo. The worst case of all is dying unwitnessed, alone and asleep, hours before anyone notices. So one of the highest-leverage, most achievable improvements to a cryonics outcome is almost boring: get notified the instant your body stops.

Which is why a cheap consumer wearable, a watch or, better, a ring, is more interesting than it looks.

The idea

Take a wearable with a blood-oxygen (SpO2) sensor. Have it sample continuously and push readings to an endpoint you control, a small Python or PHP script behind a REST API. Now you have a dead-man's switch. If the readings stop or flatline, the script can alert your cryonics standby team with your GPS location, and it can call first responders. The same alarm that summons a standby team after death could, on a survivable event like a heart attack, summon an ambulance in time to keep you alive in the first place. That is a remarkable amount of leverage from a piece of jewelry.

Why pulse-ox, and not heart rate

There is a clever argument for choosing blood oxygen specifically. A metric like heart rate can fail in a dangerous direction: a loose band or a bad contact can produce a plausible but wrong number, a false "you are fine." Pulse oximetry, the thinking goes, tends to fail the safe way. If the sensor loses contact it does not read at all, rather than inventing a comforting value. A no-read is easy to treat as "go check on this person." A false normal is the thing that kills you.

(A quick aside on what the number means, since it trips people up: SpO2 is not "your blood is 98% oxygen." It is the percentage of your hemoglobin that is currently carrying oxygen, saturation relative to capacity. Healthy people sit around 95 to 100%.)

Watches measure in the wrong place. Rings fix that.

This is the upgrade I missed when I first thought "watch." On a wrist, SpO2 and heart rate are read by the same optical sensor using the same mechanism, photoplethysmography (PPG): shining light into the skin and measuring what bounces back. Wrist optical readings are notoriously degraded by motion, a loose band, poor perfusion, cold hands, and skin tone, which is why hospital pulse oximetry uses a transmissive sensor on a fingertip, with light passing all the way through thin tissue. A watch on the back of your wrist is about the worst common spot for this.

A ring moves the sensor to the base of your finger, and that matters more than it sounds. Oura, which makes the best-known smart ring, says it measures there specifically because the blood vessels are thicker and the circulation is more concentrated than at the back of the wrist, and the company validated its SpO2 against a medical-grade pulse oximeter over thousands of hours of data. It is still reflective PPG, not a transmissive clinical clip, and no smart ring is clinical grade. But the form factor quietly answers the exact objection the wrist version runs into: it puts the sensor on the finger, where pulse oximetry is supposed to live.

Watches vs rings, concretely

If you are actually going to try this, the landscape today looks roughly like:

The catch that defeats all of them: the data is not real-time

Here is the thing that took me a minute to see. The ring fixed the sensor location, but a death-alarm does not just need a good sensor, it needs the reading in your hands within seconds. And that is where consumer wearables fall down. Oura's SpO2, for instance, is reported as a nightly average; the data syncs up to Oura's cloud and you pull it from a cloud API after the fact, not as a live, sub-minute stream you could fire an alarm on. RingConn keeps its data inside its own app. So the most accurate ring on the market still routes your vitals through a closed cloud, on the manufacturer's schedule, which is precisely the opposite of what a dead-man's switch needs.

So the wearable death-alarm has two problems: a sensor problem, which rings largely solve, and a pipeline problem, which nobody has solved in a consumer product you can just buy. The form factor moved in the right direction. The data architecture did not follow.

False alarms are still the real enemy

Whatever device you pick, the harder half is false alarms. A death-detection system has two failure modes, and they are not equal. Missing a real death is catastrophic. But crying wolf is what kills the system in practice: a standby team scrambled by a slipped band at 3 a.m. a few times will stop trusting the signal, and so will you. Good instincts for managing that:

The design target is blunt: trigger reliably on real cessation, almost never on noise.

This is already a field

Worth knowing before you reinvent it: people have been on this for years. Cryonics Monitoring has researched these sensors and devices for half a decade, the Cryonics Institute has monitoring apps, and there is active work on stranger approaches like using infrared cameras to detect the warm breath of a living person. The DIY version, a wearable and a REST endpoint, is a great way to learn the problem and prototype, but you are not alone in the woods, and the serious work has already mapped a lot of the dead ends.

What you actually want: an OPEN device

Put the two problems together and the answer hiding in the title comes into focus. The device worth wanting is finger-worn, like a ring, for the sensor, and open, with documented local or real-time data access and ideally open firmware, for the pipeline. A finger sensor you can read live, on hardware you control, with no cloud middleman deciding when, or whether, you get your own numbers. None of the mass-market options is both: the $25 watch is open-ish but the sensor and build are junk; Oura has the sensor and even an API but routes everything through its cloud on a daily cadence; RingConn is closed. The gap between "neat idea" and "a system you would stake your standby on" is exactly that missing open, real-time, finger-based device.

Practical bottom line

Automated death detection is one of the most achievable, highest-leverage upgrades to a cryonics outcome, and the survivable-emergency upside means it can pay off even if you never need the cryonics part. If you want to experiment today, a ring is the better sensor than a watch, and Oura is the most accurate option with an actual API, just understand that you are working against cloud latency and a nightly cadence, not a live feed. A $25 watch is fine for learning the plumbing. But the real target is an open, finger-worn device whose data you can read in real time and control end to end, and that is the thing the cryonics community should be pushing vendors, or itself, to build.

This is an enthusiast's practical overview, not medical advice. Consumer wearables, including Oura and RingConn, are not certified medical devices and are not validated for emergency or death detection; do not rely on one as your sole safety system. If you are building monitoring for cryonics standby, coordinate with your provider and with people who do this professionally. Thanks to the r/cryonics thread, and to Cryonics Monitoring, for the engineering reality checks.
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