11A by the component and other components RMIB multivibrator, when the old man lost not more than a certain distance, the receiver output pin output low, the time-base integrat
ed circuit NE555 multivibrator composed of its reset terminal low level circuit not oscillate, the speaker does not sound. When between the transmitter and receiver distance exceeds the pick when closed Fan trouble, RCMIB of feet high output, multi-harmonic oscillator start-up, the speaker sound newspaper blind, elderly explanation beyond a set distance. This circuit simply adjust the RP, the speaker make different sounds. The circuit is also suitable for children, mentally handicapped people. The circuit elements less, only a few dollars can be.