Useful with caveats
A trend to watch, not a number to trust
Fingertip pulse oximeter
SpO2 and pulse, fingertip clip
Useful for spotting a trend across several mornings, and actively dangerous if you treat a single reading as a verdict — cold fingers alone can drop a reading by several points, and consumer devices are not calibrated for 5,000 m.
A falling trend over days is genuinely informative
Costs very little and weighs nothing
Your guide can use it as one input among several
Cold hands produce alarming, meaningless numbers
Not accurate at the altitudes it is bought for
Encourages self-diagnosis, which is the real risk
Not for you if: Anyone who would use it to overrule how they feel or what a guide says. Symptoms decide; the number does not.
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