Looks the best location fo both rooms if its wireless you could swap it with another detector if the fault follows the detector then replace it, if the fault reoccurs in the lounge then its something environmental that your missing, I see nothing in that plan (unless you missed out some helium balloons from a recent party) that would cause fa's
I cut back the damaged cable, and spliced in a replacement section of cable, soldering the ends together before using terminal blocks.
I have full confidence in the repaired section