Ultrasonic emitting frequency: 2.5MHz±3% - Overall sensitivity at the 200 meters of distances: ≥90dB - Effective area of the ultrasonic transducer active element: 1.57cm2 - Ultrasonic output power: ＜5mW/cm2 - FHR test range: 30 bpm ~240 bpm - Battery type: 9V alkaline battery - Ultrasound gel specification: density = 1.0g/cm2 speed ≤1.7m/s - Acoustic impedance: ≤ 1.7x105g/cm2.s attenuation ≤0.02db/mm - Peak of negative acoustic pressure: p-<1MPa - Output beam sound intensity: Iob＜20mW/cm2 - Ispta＜100mW/cm2 - Backlight turns on when there is fetal heart signal; Backlight turns into white light when the fetal heart rate is between 120~160bpm; Backlight turns into orange light and the fetal doppler sounds a warning when the fetal heart rate is less than 120bpm or more than 160bpm. - No battery indicator shows in the lower right corner when the battery is at a high level; Batter indicator comes out when the battery is at a low level; When there is no cardiac value showing but only battery indicator then you need to replace the battery. - In order to hear clearer suggest not use headphones and speaker at the same time. - Now you can safely listen to the prenatal sounds and monitor the heartbeat of your unborn baby in the comfort of your own home. - Enjoy the amazing experience of hearing your baby's heartbeat hiccups & kicks. Even record them to share with family & friends.