A water-level measuring device using a gear ratio includes: a water tank filled with water; a float receiving buoyancy by being floated over a water surface of the water filled in the water tank; a cable connected to the float and extending to the outside of the water tank; a first gear connected with the cable; a second gear connected with the first gear; a weight pendulum connected with the second gear and moving in up and down directions, wherein when a water level of the water tank descends, the weight pendulum ascends due to a weight of the float, and when the water level of the water tank ascends, the weight pendulum descends due to the buoyancy of the float.

An overflow detection system for a grease trap or other receptacle is provided. The overflow detection system includes an overflow sensor. The overflow sensor can include a switch and a processor. The switch can include a float configured to float in a fluid in the receptacle, a surface that is separate from the float, and a resilient member coupled between the float and the surface. The switch can generate a signal in response to the float being within a predefined distance of (e.g., contacting) the surface. The processor can receive the signal from the switch and, in response, transmit a notification to a user device that is remote from the receptacle. The notification can indicate a high fluid level in the receptacle.

A level sensor for detecting a level of content in a tank, the level sensor comprising a flexible cable at an end of which is attached a float sensor, the float sensor configured to be suspended from the cable in the tank, in use, and to change its orientation as it contacts content in the tank, and wherein the float sensor is activated to generate a level sense indication according to its orientation.

A level sensor for detecting a level of content in a tank, the level sensor comprising a flexible cable at an end of which is attached a float sensor, the float sensor configured to be suspended from the cable in the tank, in use, and to change its orientation as it contacts content in the tank, and wherein the float sensor is activated to generate a level sense indication according to its orientation.