With excellent sensitivity, complete interchangeability and high durability, SD3 series Ultrasonic Pocket Doppler are ideal for routine fetal heart rate detection by the clinicians. Plug-and-play Compact design with easy one-hand operation Bright OLED screen with real-time FHR display 2 MHz probe with deep penetration for later pregnancy and larger patients 3 MHz probe detects fetal heart beat as early as 9 weeks Automatic power-off while putting the probe back to the rack (SD3 PLUS & SD3 PRO) Real-time monitoring for daily use Record & play with audio playback and numeric display Normal AA batteries for easy replacements Built-in Li-ion rechargeable battery ensures long working time Unique charger stand design