opposite end of the power unit attaches to a header bracket that is attached to the header wall above the garage door. The powerhead is usually supported by punched angle iron. Recently another type of opener, known as the jackshaft opener, has become more popular. This style of opener was used frequently on commercial doors but in recent years has been adapted for residential use. This style of opener consists of a motor that attaches to the side of the torsion rod and moves the door up and down by simply spinning the rod. These openers need a few extra components to function safely for residential use. These include a cable tension monitor, to detect when a cable is broken, and a separate locking mechanism to lock the door when it is fully closed. These have the advantage that they free up ceiling space that an ordinary opener and rail would occupy. These also have the disadvantage that the door must have a torsion rod to attach the motor to. Types There are five types of garage door openers: Chain drive openers. These have a chain (similar to a bicycle's) that connects the trolley to the motor. Belt drive openers use a rubber belt in place of a chain. Screw drive openers have a long screw inside the track. The trolley connects to this screw. Direct drive openers have the motor installed inside the trolley and use a gear wheel to guide the trolley along a fixed chain. Jackshaft openers mount on the wall at either end of the torsion bar. Remote control The first wireless garage door openers were invented and developed by two US inventors at the same time, one in Illinois and the other in Washington state, around 1930. They were unknown to each other. The first garage door opener remote controls were simple and consisted of a simple transmitter (the remote) and receiver which controlled the opener mechanism. The transmitter would transmit on a designated frequency; the receiver would listen for the radio signal, then open or close the garage, depending on the door position. The basic concept of this can be traced back to World War II. This type of system was used to detonate remote bombs. While novel at the time, the technology ran its course when garage door openers became popular. While the garage door remote control transmitter is low power and has