Hack Your Stress: Real-time HRV Analysis with Web Bluetooth and Polar H10

Have you ever wondered if your "flow state" is actually just high-functioning anxiety? Or why your recovery feels sluggish after a late-night coding session? The answer lies in your Heart Rate Variability (HRV). In this tutorial, we are going to build a high-performance stress monitor using the Web Bluetooth API, RxJS, and Signal Processing techniques. We'll be pulling raw RR-intervals (the time between heartbeats) directly from a Polar H10 chest strap and performing a Fast Fourier Transform (FFT) in the browser to calculate the LF/HF ratio—the gold standard for assessing Autonomic Nervous System (ANS) balance. Whether you're into biohacking, real-time data visualization, or just want to see how the Web Bluetooth API can turn a browser into a medical-grade dashboard, you’re in the right place. Pro Tip: If you're looking for more production-ready patterns on integrating wearables with enterprise cloud architectures, definitely check out the deep dives over at WellAlly Tech Blog. The Arc