The eTape Continuous Fluid Level Sensor is a solid-state sensor. Output resistance varies depending on the surface height of the fluid. It's primarily designed to be used in non-corrosive water-based liquids and dry fluids (powders). It does away with clunky mechanical floats, and easily interfaces with electronic control systems. The active sensor length is 8" (20cm).
This is only the sensor for OEM applications. It is sensitive to bending, is difficult to mount and no wires can be soldered on the connector. For these reasons, an Assembly is recommended (see below).
More information is available on the websites of Milone Technologies and Sparkfun.