Pixel Watch Loss of Pulse Detection

Loss of Pulse Detection makes Pixel Watch the first smartwatch in the United States to receive FDA clearance for cardiac arrest detection. Using a multimodal sensor algorithm, the watch can detect when a wearer's pulse has stopped and automatically call emergency services if they're unable to respond — turning an otherwise unwitnessed cardiac arrest into a witnessed one. I shipped this as part of the Personal Safety suite on Pixel Watch.

How It Works

The watch continuously monitors pulse using its green light heart rate sensor. When it detects a sudden large drop in the signal — combined with stillness on the accelerometer — it activates infrared and red light sensors for additional cross-validation. A machine learning algorithm analyzes the combined photoplethysmography (PPG) and accelerometer data across multiple verification gates before concluding that a loss of pulse has occurred.

When pulselessness is detected, the watch displays a prompt and gives the wearer approximately 15 seconds to tap "I'm OK." If there's no response, an audible alarm sounds and a countdown begins. If the user still doesn't respond, the watch automatically calls emergency services and shares the wearer's precise location.

FDA Clearance & Global Rollout

Loss of Pulse Detection launched in Europe with Pixel Watch 3 in 2024, ahead of U.S. regulatory approval. In February 2025, the feature received FDA clearance — the first time any smartwatch feature had been cleared for loss of pulse detection in the United States. The U.S. rollout followed in March 2025. The feature is now available across Austria, Belgium, Canada, Denmark, France, Germany, Ireland, Italy, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, and the United States, with more countries being added as regulatory clearance is obtained.

Safety & Validation

The algorithm was developed from training on 495 participants, validated on 298 participants, and tested on 155 participants — including testing with stunt actors using controlled pulselessness simulations. Real-world testing across hundreds of thousands of hours of wear time yielded a false positive rate of just one errant call per 21 person-years. The research was published in Nature and covered in the Resuscitation Journal, which noted that unwitnessed cardiac arrest has a survival rate 7.7× lower than witnessed events — the gap this product is designed to close.

A New Standard for Wearable Safety

Together with Fall Detection and Car Crash Detection, Loss of Pulse Detection completes a safety platform on Pixel Watch capable of autonomously recognizing and responding to life-threatening emergencies across a wide range of scenarios — falls, crashes, and cardiac events. No other smartwatch platform currently matches this combination of cleared emergency detection capabilities.

Google · Group Product Manager · Personal Safety · Pixel Watch Loss of Pulse Detection · FDA Cleared · 2024–2025