Acoustic Perimeter Calibration

I crossed the door threshold to survey the flagstone border along the pathway. A stray metallic spring clamp and a small, hollow copper plumbing sleeve lay half-buried in the crushed limestone gravel. After resting my rifle against the timber edging, I tested the clamp's tension. It held firm. I fitted the copper sleeve into the clamp's jaws and struck the metal with my armored gauntlet. A clear, high-pitched tone echoed along the gravel trench and faded into the grass. The boundary resonance is operational.