Ya that is sometimes a problem. You would think if all the pipe runs end in a heated space and you keep the pipes at the joist level it would not happen, but it does. Used duct seal on the pipes. Also moved insulation over the EMT in the atic. Realy I think is is more of an insulation in the atic issue in most cases. Have herd the ideal solution is to have the pipes go in the side of the box not the top. Maybe that would work if you could keep the pipe at the bottom of the joist deep in the insulation. Some smokes have a gasket to prevent airflow. But it still happens. Maybe a bit of fiberglass insulation in the J-bx.

The worst is when there was a problem but have no idea which one of the 10 or so devices caused it. I wish the SD would have a resetable indicator to show if that perticular one was triped.

Just herd today FireX recall on CO detectors.