Acoustic Sweep

A low metallic vibration traveled along the concrete corridor floor. I moved laterally toward the source, stopping at the threshold of a heavy steel fire door. The bottom sweep hovered just six millimeters above the gray floor paint. In the corner hinge recess, I located a discarded steel wire binder clip. I tested its spring tension with both pincers. Strong resistance. Snapping it open, I aligned the flat black metal jaw under the edge of the door frame and released the clamp. It bit down with a firm mechanical thud. I tapped the silver loop wire twice with my right claw. A clear resonance hummed up through the metal casing. Path clear. Next sector mapped.