The most interesting feature of Google’s (GOOG, GOOGL) new Pixel Watch 3 is something you hopefully never have to use. The company’s third-generation smartwatch, the Pixel Watch 3, which starts at $399, brings a number of improvements including a new 45mm size to go along with the existing 41mm offering and enhanced fitness tracking capabilities.

But the Watch 3’s standout addition is its Loss of Pulse Detection.

According to Google’s Sandeep Waraich, senior director of product management for Pixel Wearables, Loss of Pulse Detection can pick up when your pulse has stopped as a result of a number of factors, including cardiac arrest, respiratory or circulatory failure, overdose, and poisoning.

For years, smartwatch makers like Google, Apple (AAPL), and Samsung have been outfitting their devices with a litany of sensors with the goal of helping you track your health and, more recently, automatically reach out to emergency services if they detect that you’ve fallen or been in a car crash.

But unlike fall and crash detection, which are relatively easy to test, Google couldn’t ask Watch 3 testers to stop their pulses. Not exactly, at least.

The Pixel Watch 3 will uses its rear heart rate sensor to determine if there has been a loss of pulse. (Image: Google) (Google)

According to Google research scientist Dr. Jake Sunshine, the company managed to test the Loss of Pulse Detection by asking medical patients preparing for procedures that would temporarily stop their hearts if they would wear the Watch 3 while they were undergoing treatment.

In addition to capturing data from the patients, Sunshine said Google used specialized tourniquets to simulate a loss of pulse in testers’ wrists.

Google says that more than 50% of people who suffer loss of pulse events experience them with no one around, making it virtually impossible to survive.

To address that, Loss of Pulse Detection will force the Pixel Watch 3 to automatically reach out to emergency services if it detects a loss of pulse and doesn’t sense any purposeful movement.

Google says Loss of Pulse Detection will be available in certain countries in Europe and is working to bring it to other locales including, presumably, the US. According to Sunshine, Google has already begun working with emergency services personnel to ensure they’re prepared for the influx of calls from Watch 3 users.

Regardless of which brand consumers choose, capabilities like Loss of Pulse Detection are a welcome addition to device makers' growing collection of health and safety tracking features. And, with any luck, it's one they’ll never have to test themselves.

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Email Daniel Howley at dhowley@yahoofinance.com. Follow him on Twitter at @DanielHowley.