A pulse oximeter is a small, clip-like device that attaches to a body part, most commonly a finger, to measure blood oxygen levels and pulse. Here's a brief description of how it works when used on a finger:

1. Attachment: The device is clipped onto your finger, usually the index or middle finger.

2. Measurement: It uses small beams of light that pass through the blood in your finger. These beams measure the amount of oxygen in the blood by detecting changes in light absorption between oxygenated and deoxygenated blood1.

3. Readings: The pulse oximeter provides readings of your oxygen saturation levels (SpO2) and your heart rate.

It's a non-invasive, painless process and is commonly used in medical settings as well as for home monitoring.

Does that help clarify things for you?