Google Pixel Watch 3's Loss of Pulse Detection could save your life – here's how the company created it

Google Pixel Watch 3 side dial and button

(Image credit: Future/Lance Ulanoff)

Google's Pixel Watch 3 now features Loss of Pulse Detection in the US
The company has revealed how it created the feature
It's all about opportunistic detection, and preventing unwitnessed cardiac events

Google's Loss of Pulse Detection recently began rolling out to the United States after receiving clearance from health authorities in February. Now, Google has revealed how exactly it created the life-saving feature, and just what makes it so important.

The Google Pixel Watch 3 is the best Android smartwatch on the market owing to its excellent performance, stylish design, and decent battery life. At launch, it was unveiled with Loss of Pulse Detection, which can alert emergency services and bystanders if the wearer suffers a cardiac arrest.

Now, Google has revealed some of the behind-the-scenes work that went into the feature in pursuit of solving "a seemingly intractable public health challenge."

How Google made Loss of Pulse Detection

A timeline of the Google Loss of Pulse algorithm detection — (Image credit: Google)

Google says that its Loss of Pulse Detection relies on a multimodal algorithm using photoplethysmography (PPG), a process that uses light to measure the changes in blood volume, along with accelerometer data from onboard sensors.

There are multiple "gates" that must be passed because the events are so rare, and false positives are less than ideal.

Before an alert goes out, there's data from the PPG sensor (normally used to monitor your heart rate), a machine learning algorithm to check the transition from pulsatile (having a pulse) to pulseless, and further sensor checks to confirm the absence of a weak pulse using further LEDs and photodiodes.

It's all a very technical way of saying your Pixel Watch needs to be absolutely sure your heart has stopped beating before triggering an alert, rather than alerting because a user has taken off their watch, for instance.

Google says that during development it partnered with cardiac electrophysiologists and their patients, including patients with scheduled testing of implanted cardiac defibrillators, where Google measured planned temporary heart stoppages.

Google says that the other vital aspect of developing the feature, aside from accuracy, is responsibility. It detailed further the efforts it has made to minimize false positives, and also notes that skin tone is not a barrier to the efficacy of the feature.

Google also says the design accounts for maximizing battery life, using data from sensors that would already be activated to trigger subsequent further checks, rather than running a background monitoring system all the time.

The full blog is a fascinating insight and well worth the read. As noted, Loss of Pulse Detection is now available in the US, along with all the other territories it is already live in, including the UK and 14 other European countries.

Stephen Warwick is TechRadar's Fitness & Wearables writer with nearly a decade of experience covering technology, including five years as the News Editor of iMore. He's a keen fitness enthusiast and is never far from the local gym, Apple Watch at the ready, to record his latest workout. Stephen has experience writing about every facet of technology including products, services, hardware, and software. He's covered breaking news and developing stories regarding supply chains, patents and litigation, competition, politics and lobbying, the environment, and more. He's conducted interviews with industry experts in a range of fields including finance, litigation, security, and more. Outside of work, he's a massive tech and history buff with a passion for Rome Total War, reading, and music.