This circuit generates the busy tone of ordinary telephones. The transistors can be the BC548 and the components of the T filter and the multivibrator can be changed to obtain the exact tone.
This car anti-theft circuit is from a Radio Electronics magazine from May 1986. The circuit...
This circuit, well known, since it is already present in other points of this website, is from an...
We found this source with the CI 723, common at the time, in a 1989 paper. Power transistors must be...