Two-tone solar buzzer (CB20493E)

This circuit was found in a 1991 publication. The transistor can be a general-purpose type.

Ultrasonic Sensors & Transmitters (COM046E)
It can be obtained from Mouser Electronics, sensors (receivers) transmitters and benders for...
Rain Alarm (CB5366E)
This circuit appears elsewhere in this section, but taken from other sources. This is an English...
INA1650 SoundPlus Audio Line Receiver - Texas
This Texas Instruments integrated circuit, available from Mouser Electronics, has a 91 dB common...