Because they attach and release in seconds, they can be moved quickly from one place to another on autos, RV's, boats, windows, countertops... virtually any smooth, non-porous surface! The rubber pad won’t mar or damage most surfaces and helps eliminate micro vibrations produced by the vehicles engine. A spring-balanced pump ensures a consistent vacuum level and a red-line indicator warns if there is any drop in holding power. Just a few strokes on the plunger will remove the air from between the mount's vacuum pad and the mounting surface. As long as the mount maintains a reliable hold, the plunger remains partially hidden inside the pump and the red line is not visible. If the red line appears, another stroke or two will restore full holding power. A firm push or pull on the rubber tab at the edge of the pad releases the mount. Each Vacuum cup is supplied with pad protector. Vacuum cups employ the force of atmospheric pressure to grip a surface: When a vacuum exists between the cup and the surface on which it is attached, the weight of Earth's atmosphere holds the cup in place with incredible force.