Slowly, in the dark of night, the robot orbits your house. Using entirely passive "x-ray vision", without emitting telltale RF beams of its own, it builds a map of the floorplan, the furniture, and where everybody is.
It doesn't need to use an active emitter for its see-through-walls magic, you see, because it's using yours.
It's still right at the edge of SciFi, but only barely.
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