Instructions. Sonotrax a pocket fetal doppler is a hand held obstetrical unit, that is utilized in hospital, clinic and home for daily self check by pregnant woman. Important Factors Power Supply: Power Supply TWO 1.5V of AA size uses salty battery. Voltage: Voltage DC is 3.0 V. Power Consumption: Power Consumption is less than 0.8 W. Prevents anti electroshock for Internally powered Type equipment and Degree Type B applied part. Two pieces of standard 1.5V salty battery available which works for not limited than 10 hours. Standard 2M straight probe. Probes the inspection. The probe can be changed. Adds an output for headphones. The product includes Built in speaker. There is an indication for low power inspection of the battery. It has audio output that is connected to earphone or recorder with audio input.