Quads have been used as add-on equipment in security and surveillance systems for many years. Quads offer the ability to see up to four cameras in one single screen. When connected to single video input video recording devices they also allow for recording of multiple cameras onto one single source.
Multiplexers on the other hand, are versatile in the operating functions they offer. Allowing the user to see up to sixteen cameras in one single screen they also offer selection of specific camera view and other features that a quad cannot provide.
Switchers and image splitters are more commonly used by surveillance systems used by homeowners and small convenience stores.