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.