Fetal Dopplers are handheld ultrasound devices that detect fetal heartbeats (110-160 bpm) from ~12 weeks gestation using the Doppler effect 2-3 MHz waves reflect off moving heart valves, shifting frequency to audible "whooshing" via speakers. Used clinically for viability confirmation, high-risk monitoring (preeclampsia, IUGR), labor checks, and multiples differentiation; home versions reassure parents but require gel application and proper technique. Safe (low-intensity, non-thermal), contraindicated in bleeding/abdominal wounds.