This circuit was found in a Popular Electronics from the 90s. The frequency is given by R2 and C1.
We found this transistorized circuit in a 1985 documentation. The circuit can operate with...
We found this circuit in a Motorola documentation from 1978. The circuit is based on the LM324...
We found this simple alarm circuit in a 1981 documentation. As we can see, it is a car alarm...