System Sensor 4WTA-B Four Wire Smoke Detector With Built-In 135 Degree Fixed Heat Sensor & Sounder

4-wire type smoke detectors are compatible with all alarm systems, unlike the less popular 2-wire type. This model is the same as the 4wt-b model except it has a built-in sounder as well. 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 types. On the other hand, if you will have smoke detectors on more than one level and wish to label them individually, we then recommend the 4-wire type.