Pixel Watch 3 Will Be Able to Detect Loss of Heart Rate
Google has just announced that the Pixel Watch 3 ‘s “heart rate loss detection” feature has received FDA clearance and will be available to users in the US by the end of March. Read on to learn more about what this feature does, how well it works (according to one early study), and how you can enable it.
This feature is available in several European countries from the end of 2024. According to Google’s help page for the feature , it is currently available in “Austria, Belgium, Denmark, France, Germany, Ireland, Italy, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and the UK.”
What is “loss of heart rate detection”?
According to Google docs , this feature is designed to sound an alarm and contact emergency services whenever the person wearing the watch loses their pulse. According to Google’s documentation of what they had in mind when developing this feature, it could be caused by a heart attack, poisoning, overdose, or other cause of breathing or circulation failure.
When the watch detects a “lost heart rate event” (it thinks you’re wearing the watch but can’t detect a pulse using a regular heart rate sensor), the watch is programmed to do the following in the following order:
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Perform additional tests (this will take about 20 seconds) to ensure that it does not detect movement or pulse. For example, it could use brighter light in the optical heart rate sensor and check movement using accelerometers.
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Feel your wrist and ask if you’re okay. You can click the “I’m OK” button to clear the warning. This phase lasts 15 seconds.
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Sound an alarm with a 20-second countdown indicating that an emergency call will be made (“Pulse not detected/Calling 911 in…”)
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Call 911 through the watch’s LTE connection or via a connected phone and play them a recorded message (inaudible to you or others). The message states that your watch has detected a loss of heart rate and that you are not responding, along with your approximate location.
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During a call, the watch displays a “Talk to 911” button. You (or a bystander) can press this button to interrupt the recorded message and talk to emergency services like a regular phone call.
How is losing heart rate detection useful (and not useful)?
As a group of Italian health experts wrote in the journal Resuscitation , loss of pulse detection holds promise in the case of so-called “undetected” cardiac arrest. I haven’t been able to find any real description of this life-saving feature, but to be fair, it’s only been available for a few months.
Google emphasizes that this feature is not intended to provide any treatment or life-saving treatment, and certainly cannot replace the medical monitoring devices that may have been prescribed or recommended to you by your provider. It cannot prevent loss of pulse or determine the cause of loss of pulse and cannot even be sure that an emergency call will go through.
It is important to note that the heart loss detection process has not been tested in a variety of real-world situations, which may increase the risk of false positives or missing an actual event. These are some of the people who may be most interested in this feature, so it’s worth noting that this feature has not been tested for people at high risk of sudden cardiac death or for people who are pregnant, under the age of 22, have chronic pain, poor blood flow to the wrist, peripheral nerve disease, cognitive impairment, sickle cell disease, or have a tattoo on the wrist that could interfere with the sensor’s function.
How well does heart rate loss detection work on the Pixel Watch 3?
Google has published a summary of its testing of the watch as part of this document , which provides instructions for use. They tested the feature on 135 volunteers, including, according to a press release , stunt actors who simulated falls while wearing a tourniquet.
Sensitivity in clinical trials was 69.3%, meaning the feature was activated 69.3% of the time the person actually lost a pulse . In the remaining 30.7% of cases it was not activated. It’s not very good, but the idea seems to be that it’s much better than nothing.
Another measure of accuracy, specificity, Google described as “1 false positive call per 7.75 user years” with 131 of their users. (This is consistent with 131 users wearing the watches for about three weeks each, resulting in one person getting a false positive, but Google hasn’t published the full results, so we can’t say that’s how the study went or how their use compares to what you might do with your watch over the next 7.75 years.)
If you receive a false positive, you will have several chances to cancel the alert before it reaches emergency services. If you press the “I’m OK” button, the watch will ask if you did anything harmless that could have triggered it. Sleeping on your arm is one option; so they sit loosely on the watch band and don’t wear the watch at all. Google also notes that other factors, such as ambient light or pressure on the skin, can sometimes lead to false positives.
How to enable (or disable) heart rate loss detection on Pixel Watch 3
Once this feature is available here, it will be available when setting up a new watch. (This hasn’t been announced for any Fitbit models or older Pixel watches yet, just the Pixel Watch 3 in both sizes.) To enable heart rate loss detection for the Pixel Watch 3 you already own, go to the Pixel Watch app, tap Safety & Emergency , and find Heart rate loss detection . There is a switch that allows you to turn this feature on and off.