On the Oximeter...

 

Sporty's has the Checkmate Pulse Oximeter for $149.  Recommended.

 

I bought it for my wife following her being released after three weeks of ICU in 2006. A few weeks later she had complications with the onset of pneumonia, so got her into the ER post haste when noted it her oxygen saturation level dropping. 

 

Needless to say highly recommend!  Not just for flying.

 

Tracy -- fairly decent write up on Wiki on the operation.  http://en.wikipedia.org/wiki/Pulse_oximeter

 

Oh the Checkmate uses a 1/2 AA sized 3.6V lithium battery. Tadiran TLL-5902 

Radio Shack carries replacements at $20.00 (ouch). Digikey shows them for $6

each (need to save shipping and pick 'em up next time I'm up there!  :)