Simple Low Voltage Alarm Circuit schematic with explanation

This is a circuit for alarm circuit. This is a simple form circuit. This is the figure of the circuit;

This circuit can be used to monitor batteries and other volatile sources of current for problems. The circuit sounds an alarm and lights an LED, but can be interfaced to any number of other circuits for many different uses.
Part;
R1, R3 1K 1/4W Resistor
R2 5K Pot
U1 LM339 Voltage comparator IC
D1 1N5233B Zener Diode
D2 LED
BZ1 Piezo Buzzer
MISC Board, wire, socket for IC