4 wire type smoke detectors are compatible with all alarm systems, unlike the less popular 2 wire type. We're often asked which type we recommend, 2 wire type or 4 wire type. If you are going to have only a few and they will all be on one level, we recommend 2 wire type. On the other hand if you will have smoke detectors on more than one level, will have more than a four or five, or you need them with built in sounders we then recommend the 4 wire type.