Zellweger is the brand name of an electric switching device used to control off-peak electrical loads such as water heaters. It is an example of carrier current signaling. Power stations transmit a ripple signal on the main transmission lines when off-peak rates start (often around 10 pm). This ripple noise is picked up by the Zellweger, which after a random delay turns the hot water heater on. The noise is often picked up by other equipment, especially audio amplifiers and stereos and the noise can cause problems with other electrical devices. It is especially audible from ceiling fans running at low speed. Even some telephone lines can pick up the noise. The noise can be particularly obtrusive from some fluorescent light systems.