As early as the early 1980s, the infant mortality rate in the obstetric ward of a hospital in New Jersey, USA, was quite high. Late at night, the warning light on the baby monitor keeps going off for no reason. The nurses were annoyed by this, so they turned off the monitors and checked back and forth one by one.

Another example: There is a customer complaint that when a switching power supply is turned on in the computer room, the company's 100M speed LAN slows down and stops, while the 10M speed network is not affected. Turn off the power and the network returns to normal.

Later experiments found that the high-frequency interference signal of the switching power supply was coupled to the network line, causing the network to malfunction.