An electrolytic tilt sensor provides an output voltage that is proportional to the tilt angle of the sensor with reference to gravity. A typical tilt sensor has three electrodes: a common electrode and two outer electrodes. As the sensor is tilted, the electrolytic fluid inside the sensor covers more or less of the outer electrodes depending on the direction of tilt. The tilt is calculated by measuring the difference in electrical impedance between the two outer electrodes to the common.
The following links contain more information about how tilt sensors operate, typical terminology used to specify the performance or construction of tilt sensors, and how to interface electrolytic tilt sensors into an electronic circuit.