This four conductor security cable is often used to wire motion detectors, glass break detectors, and other devices that require four conductors. Two of the conductors are used for power (plus 12 VDC and ground) and the other two are used for the contact closure in the detector. (Usually a closed loop switch.)
Note that local, state, and federal building and fire codes may have specific requirements for smoke detectors. We have special wire rated for use with smoke detectors.