Valt Relay

Valt Relay broadcasts your watch's heart rate over Bluetooth, using the same standard heart rate service a chest strap uses. Anything that reads a chest strap can read your watch instead: training apps, gym equipment, bike computers. Nothing at the other end needs to know what Relay is. It keeps broadcasting when the screen turns off. Relay shows on your watch face while it runs, so you can see it is still going. You can also add it to your watch face as a complication, which shows whether it is broadcasting and opens Relay when tapped. It does not give you heart rate variability or RR intervals. HRV needs the gaps between individual heartbeats, which a wrist sensor cannot measure precisely enough. If HRV matters to you, a chest strap is still the tool for it. With the screen off, readings update every five seconds rather than every second. That is as often as the watch will deliver them while it sleeps. Reading the sensor and broadcasting continuously both use power, about as much as tracking a workout does. Tested on Samsung Galaxy watches. Other Wear OS watches should work too, but have not been confirmed yet. There is no account, no sign-in and no phone app. Relay collects nothing and has no internet access: your heart rate goes to the device you paired with and nowhere else.