Include 2*AAA BATTERIES. Easy to operate, just clip it on to your finger, press the button then will start to determine. Accurately determine your SpO2 (blood oxygen saturation levels), pulse rate and pulse strength and display it conveniently on a large digital LED display. Comes with a lanyard. Operating voltage: DC 2.6-3.6v, it will automatically shut down after 8s, if no finger inside.