Need to measure fluid levels? This eTape sensor is a solid state, continuous fluid level sensor ideal for non-nasty environments (but including water).
Want to measure the depth of something? Fluid levels, either water or powder-like? The SparkFun eTape will do this very nicely.
The eTape envelope is compressed by the hydrostatic pressure of the fluid in which it is immersed, and causes a change in decrease in resistance in proportion to the distance from the top of the sensor to the surface of the fluid. The lower the liquid level, the higher the output resistance; the higher the liquid level, the lower the output resistance.
It seems to be very similar in construction to simple keypad-pressure pads, where the squeeze makes the two halve contact, and produce a reducing resistance. Cool, and waterproof!