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The Apple Watch measures electrical voltage. Every smart ring measures light bouncing off blood. These are two different physical phenomena, and the ring form factor makes ECG impossible with current technology.
Your smart ring does not count your breaths. It counts the ripples that breathing leaves on your heart rate, then runs statistics to guess how many times you inhaled. The method is real. The precision is not.
A Stanford study tested seven fitness trackers against clinical instruments. Heart rate was accurate. Energy expenditure was off by 27 to 93 percent on every device. The calorie number on your screen is not a measurement. It is a guess.
