Pixel Watch 3 Can Now Detect When Your Heart Stops

Google has officially introduced the Loss of Pulse (LoP) detection feature to its Pixel Watch 3 lineup in the United States following FDA clearance granted earlier this year. Initially announced at the product’s launch, the feature began rolling out in March 2025 after receiving regulatory clearance in February.

The feature is designed to detect the absence of a heartbeat, potentially alerting emergency services during life-threatening situations like cardiac arrest. Unlike traditional health sensors that monitor heart rate fluctuations, LoP detection uses a specialized algorithm to identify when blood flow ceases.

To validate the functionality, Google engineers employed a simulated approach in a lab setting. Volunteers participated in tests where a pneumatic tourniquet temporarily restricted blood flow in the arm. This method aimed to replicate pulselessness without risk. The feature’s detection capabilities were then measured against these test conditions to ensure reliability.

Google published its research findings in the journal Nature, highlighting the technical groundwork and machine learning techniques used in developing LoP. According to the report, the detection system was trained on diverse data points, including variations in skin tone, age, and gender to improve accuracy across demographics.

Though the feature has received FDA clearance, it is not FDA-approved. Clearance means that the FDA recognizes the feature as substantially equivalent to existing technologies on the market, allowing it to be marketed. However, it does not confirm clinical effectiveness or comprehensive testing akin to what FDA approval entails.

Due to ethical concerns, real-world testing of such life-saving features is limited. Simulated testing remains the standard for validating performance. While the feature may not guarantee detection in every scenario, experts believe that partial effectiveness is better than no response system at all in emergency conditions.

Google Safety Team’s product manager Edward Shi noted that many cardiac incidents occur without witnesses. The LoP feature is expected to assist in such events by initiating emergency protocols autonomously, thereby increasing the chances of survival.

With the introduction of LoP, Google positions itself competitively against similar offerings from Apple and Samsung. Apple’s latest watches include fall and collision detection, while Google is focusing on unmonitored cardiac emergencies with this innovation.

The Pixel Watch 3's new health feature represents a notable step forward in wearable health monitoring. Although LoP is not foolproof, early intervention—even from an automated system—could mean the difference between life and death.