This small water sensor alarm circuit makes a loud warning sound when a humidity sensor detects a quantity of water. This circuit assembly is an application of low power comparator LM1801 made by National Semiconductor. The reference voltage for the integrated circuit is fixed with the help of R2.
When pin 4 of the LM1801 voltage exceeds preset threshold, because the moisture sensor noticed a smaller or larger chip will command the active piezoelectric buzzer with a current of over 24 mA.
In the surveillance state, the water sensor alarm circuit has a current consumption of 10 microAmps so you can use a 9V battery for almost one year. We can connect many sensors simultaneously.