A guy in a group that went up Mt. Whitney last year brought along a device that measures altitude sickness but I forget what it was called or how it works.
edit: I asked him. It was a pulse oximeter.
A pulse oximeter does not measure altitude sickness. It measures your pulse rate and your blood oxygen saturation.
Many people have an unreasonably high pulse rate when at high elevation, but it never stops them. Also, many people have an unreasonably low blood oxygen saturation, but it never stops them. It probably slows them down a lot. The oximeter can give you some indication of how close to collapse you are getting.
