The circuit is very simple and using only few external components. The speaker is derived through a BD140 transistor. Any other similar PNP transistor will work here. Make sure the 91 ohms resistor should be of 1 watt, operating voltage of the circuit is 9 to 12V DC.
Here is the project of a alarm circuit using CD4046 IC. CD4046 is a CMOS IC available in 16 lead packages. The IC can be used for many purposes for example tone decoding, signal conditioning etc. In this circuit it is used as an alarm generator. The circuit is ideal to use with project, which require alarms.