find moisture under carpet

https://future-wiki.win/index.php/What_a_Carpet_Mold_Inspection_Reveals_About_Your_Home%27s_Health

You finally decide to peel back a corner of that carpet in the basement, and your heart sinks when you spot the dark, damp patch underneath. The musty smell confirms it: moisture has been trapped there for a while, likely from a slow leak or high humidity. Now you're facing the chore of pulling up the whole section, treating the subfloor, and ensuring it dries completely before putting anything back down.