It has been known since at least the 1950s that radon is present in indoor air, and research into its effects on human health started in the early 1970s. The danger of radon exposure in dwellings received more widespread public awareness after 1984, as a result of the case of Stanley Watras, an employee at the Limerick nuclear power plant in Pennsylvania. Mr. Watras set off the radiation alarms (see Geiger counter) on his way into work for two weeks straight while authorities searched for the source of the contamination. They were shocked to find that the source was astonishingly high levels of radon in his basement and it was not related to the nuclear plant. The risks associated with living in his house were estimated to be equivalent to smoking 135 packs of cigarettes every day.