A low-frequency, op-amp oscillator and a VCO, both configured from a single MC3405 ~dual op amp and dual comparator, are tbe major components in a siren circuit tbat can be made to produce various warbles and wails, or serve as an audio sweep generator.
Linear-ic-siren - schematic

The only otber active components needed are an MPS Al3 small-signal transistor and a 2N6030 power Darlington transistor.

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