Rysky wrote:
Going off the spell it'd be a +40 before taking into account size modifiers. Since the occupant of the room is invisible the PCs might be inclined to check over the rest of the room, possibly with lots of flour so they don't get jumped.
That was my plan if there wasn't anything specific laid out. A DC 40 is steep for level ~2 adventurers, but I'll likely give them a circumstance bonus if they take more than 10 minutes to search the room.