This very low current circuit was found in the April 1995 Electronics Now magazine. The frequency should be chosen for maximum efficiency according to the small transformer used.
This protector was found in an Electronics Now from the 90s. The 250 V transient suppressors are common...
A modulated (intermittent) siren, using the four gates of integrated circuit 4001 is shown in...
This interesting circuit appeared in the April 1952 Radio Electronics magazine. The circuit is...