Mechanical Sentry

These 5-inch wooden spheres can be used to set a perimeter around a campsite, or to secure a hallway. A ring mounted on one side can be pulled to extend up to 30 feet of wire, which can be attached to either a spike or another mechanical sentry. When an intruder brushes against the taut wire, a shrill steam whistle inside the machanical sentry triggers to alert those nearby.