I bought a stud finder with metal and live wire detection (Zircon L550) mostly to trace some wires, but I also tried the metal detection feature and found something really unexpected. One end of the wall I'm detecting is part of an entryway from one room to another, there's no door frame or door hardware installed but there is a distinct "doorway", if that makes any sense. When I trace the stud finder around it, it detects metal all around the doorway but not past it (more than a couple of inches) on either side, so it seems pretty specific. I'm not detecting any metal anywhere else on the adjacent walls. I've tried recalibrating very close to it to decrease the sensitivity but it still detects metal very strongly. The house was built in the 1960s and I'm in New England.

So, what's going on? Is there any chance the doorway is framed with metal studs while the rest of the walls are wood? Am I missing something obvious?