An improved pest repellent system which results in altering the existing electromagnetic field in the electricity supply of a building by inducing a phase shift in the supply by applying a voltage to a highly inductive coil or coils in a timed pattern which pattern is offensive to pests said system comprising providing: a device including a frame at least one highly inductive coil appropriately wired within the frame and able to generate the altered electromagnetic field a solid-state circuit for controlling supply voltage to the coil(s), a timing means of controlling the timed pattern and optionally an earthing wire passing through the coil(s) to conduct said altered electromagnetic field to the environment around the device wherein said timed pattern comprises a first period where the voltage is pulsed on and off through the coil(s) resulting in a phase shift in the alternating current of the supply and a second period of equal duration to the first period where supply of voltage to the coil(s) is paused wherein the device is operated to repel pests.
