Found in na 1969 Electronics World, this circuit makes use of transistors of the time. Equivalent transistors can be used. The diodes can be 1N4004.
This alarm, from a 1996 magazine, can be fitted with two BC548s in the original configuration...
Using only one general purpose transistor this circuit is powered by batteries. The lamp of the...
Can be used as a shield, this old American documentation circuit offers digitally selected...