According to the SCOTUS Opinion in U

According to the SCOTUS opinion in U.S. v. White (1971) , involving a friend wired for sound for the police:

A) a defendant has a constitutionally protected expectation that a person with whom he or she is conversing will not reveal the conversation to the police.
B) a person contemplating illegal activities must realize and risk that a friend might be reporting to the police.
C) a suspect's friend may relate the substance of conversations between the two without violating the Fourth Amendment, but the amendment is violated if the friend records those conversations for the police without a warrant.
D) a search warrant is required any time electronic devices are used to obtain evidence.