This disclosure provides a search device, a person loss prevention system and an operation method. The person loss prevention system comprises an electronic device and the search device. The search device includes a receiver and a transmitter electrically connected with the electronic device. The person loss prevention system instructs the transmitter to transmit a predetermined signal to the receiver by the operation method. After the receiver receives the predetermined signal, the receiver sends a feedback signal to the electronic device. The electronic device adjusts a waveform of a sound signal according to the feedback signal and transmits the sound signal to the search device. The search device plays the sound signal through a speaker unit. Thereby, the user of the electronic device immediately determines the position, the distance and the direction of the receiver.