This circuit was found in the August 1994 issue of Electronics Now magazine. The 4046 is uncommon these days and the frequency range is given by C1.
This one-transistor alarm can be used with much more sensors than the two shown by the figure....
This is one of many possible configurations for this type of oscillator that generates sinusoidal...
The circuit in the Multisim Blue simulation sources a regulated voltage to loads up to 50 mA. The...