Can I add a plug to a wire-in smoke alarm and plug it into an outlet?
I have an outlet at the top of my wall, the last home owner here had one plugged in there but it's ancient (made out of metal!).

Thanks,
Lash

Do you have two wire or three wire interconnectable smoke detectors?

What is the voltage, all of my wire units the electric is converted prior to going to the alarm

If you have an older house with a 2 wire. I would suppose, yes you can. You can Also use it with a 3 wire but it will not be tied into the rest of the detectors. The simplest thing would be to use a battery unit.