Description.

This is the circuit of a comparatively strong siren useful for any purpose.A complementary transistor pair (BC 557 & 337) is arranged as an oscillator, directly drives the peaker.Transistor Q1(BC 557) is used to provide full charging of capacitor C2.When P1 is pressed, C2 discharges through R8 and the circuit starts oscillating at a low frequency that increases slowly until a high frequency steady tone is reached and it is kept.When P2 is released C2 starts discharging and and output frequency slowly decreases.When C2 is charged fully the circuit stops oscillations.

Tips.

Adjust the values of C2 & R6 to vary the tune.Wire the circuit on a good quality PCB.A good quality common board may also do trick.

 Parts List.

R1,R3_________1K  1/4W Resistors
R2,R5_________10K  1/4W Resistors
R4___________220R  1/4W Resistor
R6___________220K  1/4W Resistor
R7___________22K  1/4W Resistor
R8___________100K  1/4W Resistor

C1,C2_________22µF  25V Electrolytic Capacitors
C3___________10nF  63V Polyester or Ceramic Capacitor
C4___________47µF  25V Electrolytic Capacitor

Q1,Q2________BC557   Transistors
Q3__________ BC337   Transistor

SW1________   SPST  Toggle or Slide  Switch

P1__________  SPST  Pushbutton  Switch

SPKR________8 Ohm speaker

B1__________ 12V Battery

Circuit Diagram .Click to Enlarge.