Regarding the possibility of the Earth remaining hidden from detection by alien civilizations by running silent, New Scientist points out that it’s already too late (Shostak, Seth, “It’s Too Late to Worry That the Aliens Will Find Us,” 3 July 2010):
We have been inadvertently betraying our presence for 60 years with our television, radio and radar transmissions. The earliest episodes of I Love Lucy have washed over 6,000 or so star systems, and are reaching new audiences at the rate of one solar system a day. If there are sentient beings out there, the signals will reach them.
(Related: “The Noosphere Visualized,” 1 January 2009)