Definition
A small electronic device that measures the percentage of oxygen saturation in the blood (SpO2) and the pulse rate by shining light through a fingertip or earlobe.
Plain English
A clip-on device, usually worn on a fingertip, that shows how much oxygen is in your blood and how fast your heart is beating.
Context Anchor
Seen in high-altitude flying and oxygen-system discussions, especially when checking whether supplemental oxygen is keeping the pilot adequately supplied with oxygen.
Derivation
From 'pulse' (the heartbeat felt in the arteries) and 'oximeter' (a device that measures oxygen). 'Oxi-' comes from oxygen, and '-meter' from the Greek 'metron' meaning 'measure.' So literally: a device that measures oxygen and pulse.
Why Pilots Care
Early detection of falling oxygen saturation prevents hypoxia before noticeable symptoms impair judgment or performance.
Intuition Check
A pulse oximeter does not measure how much oxygen is in the aircraft’s oxygen bottle. It estimates how much oxygen is being carried in the pilot’s blood.
Example Sentence 1
Cruising at 12,500 feet, the pilot checked the pulse oximeter and saw her oxygen saturation had dropped to 88 percent, so she put on her cannula.
Example Sentence 2
After donning the oxygen mask the student checked the pulse oximeter reading to confirm saturation above 95 percent.