I measured my stress simultaneously with an Android stress check app and the emWave2 and I found a decent correlation between my Coherence scores and the app's stress score. So I do recommend trying the heart rate variability smartphone app.
However, the major difference is that the emWave2 is an actual biofeedback device and it provides immediate HRV feedback. Also, you also don't have to worry about the EmWave2 burning your finger!
Read more 馃搼 about the Heartmath emWave2
https://www.limitlessmindset.com/mind-hardware/379-heartmath-emwave2
馃摫 Get the HRV stress test app
https://www.limitlessmindset.com/Stress-Test-App
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