I am building my basement right now and have been reading about wiring and circuits. I thought I had everything figured out for my basement until I started looking into my lighting circuit today. I had a circuit that I thought I could easily add to, to handle my needs. I will be adding three bedrooms and a family room. I will probably still be OK, but I will really have to reduce the number of recessed lights in my family room.

Here's my problem though. I noticed that my smoke detectors are also run on my lighting circuit. While this is common to have them wired on a lighting circuit, I can't find anything that says how many watts a smoke detector consumes. I currently have 6 smokes upstairs that are on this circuit and one downstairs. I will be adding 4 more downstairs and need to know how they will affect how many lights I can have. The lights are all wired with 14/2 wire, and the smokes with 14/3. I need to know how many watts smokes consume so I can properly figure out how many lights I can have on the circuit without overloading it.

No one ever asked, so I had to look, and I see what you mean, I cannot find any load ratings for several of the popular manufacturers of smoke alarms. Most do state not to interconnect more than 18, but I think this is due to the limit of the inteconnecting switch. The load of a SD must be extremely low, not to have it published on product spec sheets.

Do not worry about the load of the detectors. You need to be cautious of the amount of lighting on one circuit. A 15 Amp circuit can handle a total of 1800 watts. In commercial, we derate that by 80%, bringing the total load down to 1440 watts, and usually use that in residential, as a safety factor.

The 80% rule is for anything that operates 3 hours or more, which is unlikely in homes.

Also, all bedroom wiring must be protected with an ARC Fault circuit breaker,
And not the smoke detectors on that wiring. So install a separate Arc Fault circuit for the bedrooms, and leave the detectors on the original circuit.