The VCR will record whatever is on the screen at any given time. Most switchers allow an alarm input, like a panic switch, to go directly to a camera which has been activated. A switcher is the least expensive of the three. No recording of any other camera while one is in alarm Quads A quad is used to show up to four cameras on the screen at once. A two- page quad switches between two different sets of four cameras each.
Quads are also able to have alarms bring one camera up full screen.
Some quads will allow you to zoom in on one camera on playback. A quad is priced right in the middle of the three. Multiplexers A multiplexer offers the best of both worlds. It is possible to view all the cameras on the screen at the same time, but the image is actually recorded full screen. Multiplexers are available in sizes from four to sixteen cameras.