This is the diagram of heat detector circuit which already integrated with siren circuit in the output. This circuit applies a complementary pair comprising NPN metallic transistor T1 (BC109) and PNP germanium transistor T2 (AC188) to detect heat (because of outbreak of fire, for example) in the area and activate a siren/alarm. The collector of transistor T1 is joined towards the base of transistor T2, while the collector of transistor T2 is joined to relay RL1.
The 2nd section of the circuit consists of well-known IC UM3561 (a siren and machine-gun sound generator IC), which is able to generate the sound of a fire-brigade siren. Pin numbers 5 and 6 of the IC are joined towards the +3V supply once the relay is in activated state, whereas pin 2 is grounded. A resistor (R2) joined across pins 7 and 8 is utilized to deal with the frequency of the inbuilt oscillator. The output is obtainable from pin 3.
Two transistors BC147 (T3) and BEL187 (T4) are joined in Darlington configuration to boost the sound from UM3561. Resistor R4 in series with a 3V zener is utilized to deliver the 3V supply to UM3561 when the relay is in activated state. LED1, joined in series with 68-ohm resistor R1 across resistor R4, glows once the siren/alarm is activated.
To check the operating of this circuit, provide a burning matchstick near to transistor T1 (BC109), that causes the resistance of its emitter-collector junction to go low because of an increase in temperature and it will begin conducting. At the same time, transistor T2 also conducts since its base is joined to the collector of transistor T1. Because of this, relay RL1 activates and switches on the siren circuit to generate loud sound of a fire-brigade alarm.
Below table is the possible sound effects generated by UM3561:
This heat detector + siren circuit already tested and it is working.