A pulse oximeter is a small, non-invasive device used to measure the oxygen saturation level in a person's blood. It typically clips onto a fingertip and uses light sensors to determine how much oxygen is being carried by red blood cells. This information is crucial for assessing respiratory function and overall health. The device is commonly used in hospitals, clinics, and even at home for patients with conditions like asthma or COPD. By providing real-time data, a pulse oximeter helps healthcare providers monitor a patient's oxygen levels and make informed decisions about treatment.