Altimeters

Manufacturers of skydiving altimeters.

An altimeter tells you how far above the ground you are. This is essential information so that you can open your parachute before you hit the ground.

"Audible altimeters" make a sound at a pre-programmed height(s), e.g. the height where you should pull your parachute, or for formation skydivers "break-off" height where you start moving away from the other skydivers to prevent mid-air collisions when you open your parachute.

(Note that "Skydiving" and "Parachuting" mean the same thing).