There's some customization to how it behaves, but you can just turn it on and put a finger in, and it works fine. Note that I had to check with my PCP on this, as the SpO2 numbers ended up being consistent but usually 1-2 lower than what a more-professional reader would produce. It's not an actual issue, but I hover right at the point where this device alerts me of potentially-low levels, but in reality I'm fine.
Rating: [5 of 5 Stars!]