security mounting question

If I am adding a smoke detector to my hardwired security system along with a new siren like a system horn only, would I need an old work back box like the plastic ones or do I not even need one because I know for low voltage applications like CATV and DATA you don’t need one, and the code stated that any device that has brackets for mounting that is low voltage does not need one. just want to check?

In all honesty, I’m not sure if it’s really code requirement or not. When talking about residential applications, I’ve always mounted smokes to back boxes. I’ve seen them surfaced mounted but don’t like that. Looks hacked, plus you end up pinching the wires trying the get the smoke back on the base. Things like sirens, keypads, etc, I wouldn’t worry about. I would just go ahead and cut one in. Not much trouble at all.