This Flood Sensor takes 2 CR2032 batteries and the typical battery life for the sensor is 3-5 years.
1.
Remove the outer cover by pressing in on the rectangular end on the front pointed end of the sensor.
2.
Replace the two CR2032 batteries by sliding them out of their metal compartments. Install new batteries with positive ends facing up.
3.
When complete, please ensure the cover is place back on the front face of the sensor