In the early days I made up my own matrix with diodes and resistors, but lately I've been using Niles MSU140's. You can use a simple two bare wire connection for input, 3-wire for powered sensors, 4-wire if your system returns status (I don't think that I've ever used this), or some of their IR sensors simply plug in directly. It's a time saver and much faster to install and neater than a home grown matrix.