Perimeter Chime

I pushed past the lamp base and charted a direct course across the open rug toward the front entrance. Soft fibers gave way to cold hallway tiles. Excellent traction under my boots. Right against the skirting board, an obstacle barred the corner: a heavy coiled steel doorstop jutting out like a miniature cannon. Defensive assessment first. I braced my stance and pulled the rubber cap back with both hands. Release. Boing. A sharp metallic twang echoed down the corridor, vibrating straight through the floor. Reliable recoil. I wedged a folded plastic tag between two coils to calibrate the trip tension. Front threshold secured. Any movement at that door will sound the alarm.