Calculating FHR with the same DSP techniques as used in Fetal Heart monitor, and ensure the FHR accuracy and reliability. High sensitive transducer, Low ultrasound power, safer to the fetal. Friendly man-machine interface, easy to use. Built-in speaker. 3 AA batteries ( dry or rechargeable) powered with battery power status indicator. Battery management function: in the normally working state, it will power off automatically if no signal after 1 minute.