It requires two AAA batteries, which are included.
When using your GPD Health Pulse Oximeter, keep your hands still in order to get the most accurate results. Please contact your healthcare provider if you are experiencing any unusual symptoms related to breathing or if your readings are outside of ranges established by your healthcare provider. Adjustable brightness helps you see the numbers clearly even in low light. Place one of your fingers inside to the end, then press down on the switch button once, located on the front panel, to turn the unit on.