Install electrical wires from the electrical panel or fuse box to the smoke detectors. First, run a 12-2 NMB with ground wire from the panel to the first box. This will give you a hot, neutral and ground wire. Mark "hot wire" on this piece of wire at the box.
Next, run a 12-3 NMB wire with ground from the first box to the second box. If there are more than two boxes, run a 12-3 NMB with ground wire to each of these boxes also. No box should have more than two wires in it when you are finished.
