This circuit from Popular Electronics powers a small speaker. The transistor can be of general use and the capacitors can be altered to change the sound generated.
This remote control receiver via the power grid appears elsewhere on this site from other sources....
May 2017 - Torex's XBP14E5UFN, an array of TVS circuit protection diodes with only 0.8 pF of...
This circuit was suggested by Electronic Engineering in a 1980s publication. The circuit makes use...