I'm only real familiar with the rubber ones that Overhead Door uses, and they're pretty primitive. The bumper edge is hollow inside, and is airtight. The tube goes up to a pressure switch. When the pressure switch gets a "jolt" from the air in the edge getting compressed, it makes an electrical contact to send the door back up. Much like the bell from the hose you drive over at a service station. These sorta stink in harsh environments, because if they get snagged or ripped, they'll "leak" and not work when you need them. The other one looks similar but is all electric. The rubber bumper has two metal strips running the full length, and they touch when the rubber gets compressed. These can get pretty shredded up and still work fine.