Components List:

R1,R5___________ 4.7K
R2______________ 47K
R3______________ 10K
R4______________ 100K
Rx______________ *see text

C1,C4__________ 100uF/25V, electrolytic
C2,C3__________ 0.01uF (10nF), ceramic
T1_____________ 2N3702 (NTE159, TUP, etc.)
IC1,IC2________ LM/NE555, MC1455P, etc
LS_____________ Loudspeaker

This alarm circuit uses timer IC to generate frequency. The circuit has wide range supply voltage 5V to 15V DC.

*The Loudspeaker LS and the resistor marked “Rx” should be together 75 ohms. If you have a standard 8-ohm speaker then Rx is 67 ohms. The nearest value is 68 ohms. So for a 8 ohm loudspeaker Rx is 68 ohms. For a 4 ohm loudspeaker Rx is 71 ohms, for a 25 ohm loudspeaker Rx is 50 ohms, etc.

circuit diagram by Tony van Roon,
source: http://www.sentex.ca/~mec1995/circ/wailing.htm

Components List:

A multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as light emitting diodes, timers and flip-flops. The monostable multivibrator will create a condition: in which one of the states is stable, but the other is not?the circuit will flip into the unstable state for a determined period, but will eventually return to the stable state. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a one shot. A common application is in eliminating switch bounce.

R1  : read the explanation
C1  : read the explanation
C2  : 10nF
IC1 : Timer IC LM555

Notes:

• R1 and C1 determine length of output pulse where t = R1 x C1 and R1 is in ohms and C1 is in farads. You may determine the value of R1 and C1 to get the frequency needed.
• Pin 4 is the RESET. Leave it connected to power supply (+V) during normal operation. Bring pin 4 AND pin 2 low at the same time to reset timing cycle.