Light-based oxygen monitoring — and why it beeps falsely.
The small device on your finger is called a pulse oximeter. It shines two beams of light through your skin to measure the color of your blood. Red blood cells carrying oxygen absorb light differently than cells without oxygen. The sensor calculates your oxygen saturation, which is the percentage of oxygen in your bloodstream.
The sensor detects the rhythmic surge of blood with every heartbeat. This allows the machine to display your pulse rate alongside your oxygen level. By confirming a steady pulse, the device ensures it is reading a live signal rather than background noise. A consistent pulse wave confirms the sensor is placed correctly on your finger.
False alarms often happen because the sensor cannot get a clean reading. Cold hands, poor circulation, or fingernail polish can block the light beams from passing through your finger. Moving your hand or shivering makes it difficult for the device to track the pulse rhythm. When the signal quality drops, the machine alerts staff to check the connection.
A normal reading is typically between 95 and 100 percent for a healthy adult. If your levels drop, the machine sounds an alarm to alert your nursing team. We treat the patient, not just the monitor, so we will always assess your breathing and comfort level before assuming the number is accurate. You can usually ignore the beeping while we adjust the sensor.