BLE Heart Rate Zones
A browser-based heart rate monitor with zone tracking over Bluetooth LE
Gym equipment with heart rate displays on the handles has existed for decades. The idea is sound: keep your eyes on a number, stay in a zone, train with intent rather than by feel. But those sensors are unreliable and most people already carry a far more accurate device on their wrist. The problem is that checking a watch mid-set – or mid-elliptical stride – breaks focus and doesn't give you the continuous feedback that actually changes how you train.
I was doing a lot of elliptical sessions in early 2026, working within specific heart rate zones and wanting to maintain a stable HR over several minutes without constantly glancing down. My Garmin Forerunner 55 can broadcast heart rate over Bluetooth LE. I was already using that feature in Beat Saber on my Meta Quest 3. My PC has a Bluetooth receiver. The gap between those two facts and a working monitor was a browser's Web Bluetooth API and a morning with an LLM.
heart.jahus.net connects directly to any BLE heart rate sensor from the browser. No app, no install, no pairing ritual. The interface shows a live zone dial and a trend graph. Zones are fully configurable: custom boundaries, names, and colors; all saved in browser storage. The tool handles reconnection on signal loss, which turned out to matter more than expected during longer sessions with my watch.
It works with any device that broadcasts the standard BLE Heart Rate profile: Polar H10 (most chest straps) and Garmin devices in broadcast mode (most smart watches). Everything runs client-side.
DarthJahus