Product DescriptionPower: 2 AA batteries (no included) Ultrasound frequency: 3MHz Ultrasound intensity: 10mW/cm2 Dimension: 135 95 35mm FeaturesThe ultrasound is lower than the national ultrasonic power standard by over 50% above, 0 radiation. Compact and portable design provides a convenient use and carrying. Loud speaker, built-in speaker gives clear and loud voice. Automatic shutdown function in case of no work High sensibility, may detect the heartbeat as early as 12 weeks, able to detect in 16 weeks for most of the case Three calculation modes to calculate fetal heart rate: instant, 10 second average and manualHow To Use1.Insert batteries if you havent done so2.Lie back in a comfortable position3.Apply the gel to your lower belly4.Turn the doppler on (by press and hold the power button few seconds) and slowly move the probe around until you can hear the steady heartbeat sounds (similar to train track sound)5.The earlier it is in your pregnancy, the lower youll likely have to go6.Be aware that you may also hear the fragment pulse of an artery (in the range of 60-100 BPM). Fetal heartbeat is continues and much faster (in the range of 120-160 BPM)