Hi Alan, most snake repellers operate by generating vibrations through the ground that snakes are supposed to find discomforting. We don’t know of any sound scientific basis for these repellers to work but there is much evidence that they don’t work. According to anecdotal evidence, they may work under certain circumstances with certain snake species, but generally they don’t seem to deter snakes at all.
The best way to deter snakes is to make the environment around the house as unappealling as possible. This involves removing long grass, eliminating prey (such as rodents), removing sheets of tin and wood piles on the ground, and removing access to water bodies near the house.