A strange rectangular apparatus that allows anyone the ability to see through walls

The second floor of the abandoned house was even more run-down than the first, with holes in the floor as big as housecats. Lucy could barely see by the scant sunlight that filtered in through cracks in the roof. Lucy took a moment to get her bearings. She could still feel the key's location; it was to the north, and it was close. In the neighboring house, in fact. There was a window that was leading right to it in one of the rooms across from the top of the banister, which she was now standing at the top of. Lucy carefully began climbing off the banister, until she was back on the floor, and then made for the window...