Works well; but has a high current draw, so batteries don't last long even if they're not used much. In contrast, the battery in my old Nonin oximeter lasted half a year with occasional use. I have to take the batteries out or they won't last a month. Data is only saved when prompted via the cumbersome menu, which means you have to be fully awake to operate the menu, so you can't take measurements upon waking, which are important for checking electrolyte balance (primarily potassium), sleepβ¦