A liquid level sensor is an electronic device used to measure the height of liquid in a container. The sensors measure the liquid level by measuring the electrical resistance between two metal probes. This resistance changes with the level of liquid - when the probes are submerged in liquid, the electrical resistance increases. The liquid level sensors are designed to accurately and quickly measure the level of liquid in the container. There are many types of liquid level sensors available on the market, ranging from mechanical float switches to digital optical/ultrasonic sensors. They are typically installed in tanks, reservoirs, and ponds to measure and monitor liquid levels.