Underwater buttons

Most camera cases, etc. use a regular mechanical switch, with a fair amount of resistance, running through a series of O-rings. That switch pushes an electronic button or something on the inside. It’s a pain in the ass to have to grease and clean o-rings all the time, though, so that’s probably not an ideal system.

Some diving equipment (lights, computers, propulsion units) uses magnetic switches due to the completely hermetic construction. These can range from momentary push buttons to sliders or even rotating knobs. For tactile feedback, the mechanical parts of the switch can reside outside the pressurized housing, mitigating pressure effects on moving seals. Underwater electronics usually have electronics coated or epoxy potted at the very least, sometimes pressurized and filled with oil. Are you thinking of data entry or switching functions?