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arXiv · 2606.21436

Pixel Watch: Robust Heart Rate Sensing from Multipath PPG and On-Device Deep Learning Trained on 10,000 hours of Free-Living and Fitness Data

Daniel Roggen·Megan Walker·Yojan Patel·Shyam Tailor·Dimitris Spathis·Matt Wimmer·Brennan Garrett·Dan Howe·Abhinuv Pitale·Hamed Vavadi·Tien Le·Steve Diamond·Oleksiy Vyalov·Vik Sharma·Pete Richards·Tracy Giest·Erika Siegel·Tuan Phan·Sam Mravca·Derrick Vickers·Benjamin Stone·Katarina Vukosavljevic·Justin Phillips·YongSuk Cho·Stefanie Hollidge·Antony Siahaan·Soren Brage·Shwetak Patel·Robert Harle
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Abstract

The Pixel Watch 2 (PW2) is the first Google smartwatch to combine multipath photoplethysmography (PPG) with deep learning-based heart rate inference, designed to significantly improve sensing accuracy during motion-heavy activities. The device processes 10 optical channels using an on-device, 15-layer temporally dilated convolutional neural network (~300K parameters) to yield a 1 Hz heart rate output. Crucial to this model's performance was its training on a massive dataset comprising 10,000 hours of data from 962 participants, curated from a broader corpus of controlled and free-living activities. We evaluated the PW2's sensing performance across two independent validation sets: an in-house fitness dataset (229 participants, 250 hours) and an external free-living dataset (27 participants, 1000+ hours). The system achieved 95% Limits of Agreement of -10.34 to 8.66 BPM during exercise and -6.57 to 7.48 BPM during free-living activities, demonstrating substantially tighter error margins than previous Google devices. Finally, we discuss key design lessons, emphasizing that large-scale deep learning was instrumental in fully leveraging multipath PPG hardware over traditional signal processing approaches.

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Daniel Roggen, Megan Walker, Yojan Patel, Shyam Tailor, Dimitris Spathis, Matt Wimmer, Brennan Garrett, Dan Howe, Abhinuv Pitale, Hamed Vavadi, Tien Le, Steve Diamond, Oleksiy Vyalov, Vik Sharma, Pete Richards, Tracy Giest, Erika Siegel, Tuan Phan, Sam Mravca, Derrick Vickers, Benjamin Stone, Katarina Vukosavljevic, Justin Phillips, YongSuk Cho, Stefanie Hollidge, Antony Siahaan, Soren Brage, Shwetak Patel, Robert Harle. 2026-06-19. Pixel Watch: Robust Heart Rate Sensing from Multipath PPG and On-Device Deep Learning Trained on 10,000 hours of Free-Living and Fitness Data. https://doi.org/10.1109/lsens.2026.3694237

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