How Smartwatch Stress Tracking Actually Works in 2025: The Science Behind HRV and Accuracy
Smartwatches don’t “read your mind.” They watch your heartbeats—specifically, the tiny time gaps from one beat to the next—and then use math to guess how revved-up (sympathetic) or relaxed (parasympathetic) your nervous system is. That core signal is heart-rate variability (HRV). In 2025, most watches estimate HRV from the optical sensor on your wrist (PPG), … Read more