Lost alarm circuit for the elderly

The multivibrator is composed of components such as component 11A
and RMIB . When the old man is lost within a certain distance, the receiver output pin ③ outputs low level. The multivibrator composed of the time base integrated circuit NE555 and other components has its reset terminal. ④ is low level, the circuit does not vibrate and the speaker does not produce sound.     When the distance between the transmitter and the receiver exceeds the receiving range, the ③ pin of RCMIB outputs a high level, the multivibrator starts to vibrate, and the speaker emits a beeping sound, indicating that the old man has exceeded the set distance. This circuit only needs to adjust RP to make the speaker produce different sounds. This circuit is also suitable for children and mentally retarded people. This circuit has few components and only costs a few yuan.