Most float switches use a magnet which triggers a reed switch. On a stem mounted float switch the magnet is contained in the floating portion while the reed switch resides in the main body. This allows the reed switch to be triggered without needing any direct physical connection between the floating portion and the switch. Such designs allow for the floating portion to move freely without getting stuck and doesn’t require waterproofing any moving linkages.

On a cable mounted float switch the magnet and switch reside in the same waterproof body. The body floats on the surface while the cable pulls the body up or down. The magnet falls towards or away from the switch depending on the angle of the body, which changes with the liquids level. This design can also use a counterweight to pull the cable down at different lengths, which allows one to set the level at which the switch actuates. They also tend to have greater hysteresis (additional change needed to turn the switch off after it was turned on).