I use the CMS Model 50-E Pulse Oximeter. It can be bought in hundreds of online stores and has a bunch of features I found neat but I never use. I have a second cheaper Oximeter the CMS-50D which is 1/2 the cost and works just fine too.
Item is hard to break, and the battery last a long time on the shelve and recharges on a USB cable off a PC if desired.
Both models are easy to use and have clear large displays perfect for the airplane.
Safety: Pulse Oximeter
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