This power failure alarm project is a power supply monitoring
device that will trigger a buzzer when the mains supply cuts
off. At the same time, the light emitting diode will be turned
ON. This device is helpful to inform the loss of power supply to
some critical installation such as a pump in a fish tank. Once
the buzzer sound, you will know that there is a loss of power
supply and actions need to be taken to rectify the situation by
providing alternative power supply or relocating the
installation. The circuit shown below consists of a AC relay. If
the mains input is 120V AC, use a 120V AC relay. If the mains
input is 240V AC, use a 240V AC relay. The relay is a Single
Pole Double Throw (SPDT) type where the COM will be connected to
NC terminal if it is not energized Once energized, the COM
terminal will be connected to the NO terminal. This type of
relay is commonly available from any electronics shop. Make sure
that the coil of the relay rating is rated according to your
mains power supply. Improper rati