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.