Atsusa*

Atsusa lab

Heat cascade simulator

Heat illness builds before you feel it. Put in your own heart rate numbers, pick a session and the weather, and see the exact minute Atsusa would warn you. Everything runs in your browser: no account, no data leaves this page.

Atsusa is an app for Apple Watch and iPhone. It watches your heart rate against the real heat around you and taps your wrist before heat illness sets in. This page shows you what it would have seen.

* Atsusa is in beta: in tester rounds now on iPhone + Apple Watch.

  • Your heart rate against the real heat
  • A warning before you feel it
  • On your wrist, running in the background

1. Your baseline

Numbers stay in your browser. Nothing is sent anywhere.

Context only. No location access, no lookup.

Sit quietly for two minutes, then read it off your watch.

Most smartwatches show this. Unsure? 40 low, 65 average, 90 fit.

Your heart rate on a relaxed five minute walk.

Measured, or estimate it as 220 minus your age.

Your timeline appears here

Your result appears once you run the plan.

* Atsusa is in beta: in tester rounds now on iPhone + Apple Watch. A research prototype. Atsusa is an early warning, not a medical device, and the thresholds here are a working hypothesis we are still tuning. More about Atsusa