If you want an up-down swept frequency instead of the nee-naw siren sound you could try this circuit :-
View attachment 118873
U1a and U1b create a large amplitude slow up-down ramp which modulates the frequency of a sawtooth tone generated by U1c. (Without D1 the duty cycle, rather than the frequency, would be modulated).
Inputs of the three unused gates of the CD40106 package should be grounded.
I've attached a siren.wav file of the sound it generates. (Delete the .txt extension). Also attached is the LTspice simulation file.
What is U1a U1b U1c ?