## Stress Tracking Devices > Another feature worth noting is the all-day stress tracking. The way this works is by measuring your HRV (or heart rate variability) data using Firstbeat technology. What’s really interesting about this feature is that you’ll actually get a “relaxation reminder” if your stress levels get too high during the day. The tracker actually vibrates when this happens and then walks you through a 5-min breathing exercise. I have to say I was wildly impressed by this feature, especially for the low cost of this device. Well done, Garmin. https://medium.com/@katietypea/the-24-7-stress-tracking-smartwatch-too-good-to-be-true-661d13cbc525 > Heart rate variability measurements used by HRV Tracker are calculated by measuring the variation between individual heartbeats. Your Apple Watch automatically measures your HRV in the background and stores the outcome into HealthKit. HealthKit uses SDNN heart rate variability, which is calculated using the standard deviation of the inter-beat (RR) intervals between normal heartbeats (measured in milliseconds). Besides background measurements generated automatically by your Apple Watch you can use the Breathe app on your Apple Watch to generate new measurements. https://apps.apple.com/de/app/hrv-tracker-for-watch/id1463020956#?platform=appleWatch > Stress can be primarily detected with monitoring HRV (Heart Rate Variability) and can yield 90% accuracy according to some studies. https://www.myhealthyapple.com/wearables-offering-stress-detection-management/ https://www.myhealthyapple.com/stanford-wearable-stress-sensor/ ## Arduino Hacking - https://www.youtube.com/watch?v=aEAqb7rIzeM - https://m.gearbest.com/smart-watches/pp_1232618.html?vip=19922732&gclid=CjwKCAjw0N3nBRBvEiwAHMwvNmgATyXIT-tjTOA_8I8bK9ZVdcK3_rS8rxNOwzCy8kIYOmlLAp976RoCRbAQAvD_BwE it can be program via Bluetooth without opening it search for D6Flasher on play store - http://atcnetz.blogspot.com/2019/02/arduino-auf-dem-fitness-tracker-dank.html - https://www.mikrocontroller.net/topic/467136 - https://github.com/sandeepmistry/arduino-nRF5