The dog and the collar
One man has established a special system to his dog hasn’t run away with the plot: a fence with sensors and collar. The essence of the device is that when approaching the fence, the collar starts beeping.
If the dog will run out of bounds, it will hit the weak discharge current. The story of a neighbor: “Every morning the dog comes to the fence, the collar starts beeping. The dog waits for discharged battery from the sound in the collar and then the dog runs away…”