This circuit was found in a publication by Edelman from 1924. The power comes from the battery and the listening is through a high-impedance headphone.
This circuit was found in a 1967 Electronic Design. The circuit makes use of components from the...
This alarm circuit was found in April 1975 Radio Electronics magazine. The circuit uses a 12 V...
This latching alarm using simple contact relay was found in an English documentation from 1980. The...