I don't know about a lay-person, but any government agent (police, a tv-detector-van driver, whatever) cannot act on the results of a search that was done witho

I don't know about a lay-person, but any government agent (police, a tv-detector-van driver, whatever) cannot act on the results of a search that was done without a warrant (or probable cause and some exigency). People's houses are especially sacred in US law and even flying a plane over and looking for excessive heat signatures to find Marijuana growers was deemed an illegal search (someone linked to that case in another comment)