The earliest versions of garage door opener controls were much simpler than today's machines- they consisted of a transmitter, also known as the remote, and the receiver, which was in charge of telling the opener mechanism to begin operating. The transmitter was supposed to only propagate a signal on a certain frequency, and the receiver would get it much like a radio signal.
The main idea for this function is rooted in technology developed during World War II. Originally, this radio transmitter/receiver/function system was utilized to detonate remote-controlled bombs. Luckily, in your home, the receiver is only signaling to a garage door, not a bunch of C-4 o dynamite.
The problem was, there weren't enough unique frequencies to make sure that remotes wouldn't be able to open garage doors that they didn't belong to. Lots of transmitters would interfere with receivers throughout the area.
The next wave of wireless openers also had something of an interfering frequency problem, which was rectified by making the garage door opener owner choose and set a code by way of dip switches on both pieces of equipment. This only provided 256 different codes and therefore was not very high security.
The third group of garage door opener technologies consisted of a larger frequency range that went froun three hundred to four hundred mega-hertz, with reliance on rolling code technology that changed a transmitter's code hourly.
And the latest versions are highly similar to this, but with a more specific frequency range that avoids any interference from the radio system (LMRS) that the U.S. Military uses.