The unit emits a low frequency vibration every 15-20 seconds, which is transmitted through the soil. Covers up to 9000 sq. Ft. (about 836 sq. metres). Battery operated (4 x D cell batteries). Safe and economical to run. Environmentally friendly - no chemicals or traps. The only mole repeller to include both a flower-bed cap and a flat mow-over lawn cap. Will not affect humans, cats, dogs, fish or birds.