“ It may also be that with the recording in existence it is less likely that the informant will change his mind, less chance that threat or injury will suppress unfavorable evidence and less chance that cross-examination will confound the testimony. Considerations like these obviously do not favor the defendant, but we are not prepared to hold that a defendant who has no constitutional right to exclude the informer's unaided testimony nevertheless has a Fourth Amendment privilege against a more accurate version of the events in question. ”

“ The issue before us is whether the Fourth Amendment bars from evidence the testimony of governmental agents who related certain conversations which had occurred between defendant White and a government informant, Harvey Jackson, and which the agents overheard by monitoring the frequency of a radio transmitter carried by Jackson and concealed on his person. ”

“ The Court of Appeals understood Katz to render inadmissible against White the agents' testimony concerning conversations that Jackson broadcast to them. We cannot agree. Katz involved no revelation to the Government by a party to conversations with the defendant nor did the Court indicate in any way that a defendant has a justifiable and constitutionally protected expectation that a person with whom he is conversing will not then or later reveal the conversation to the police. ”

“ Inescapably, one contemplating illegal activities must realize and risk that his companions may be reporting to the police. If he sufficiently doubts their trustworthiness, the association will very probably end or never materialize. ”

“ But if he has no doubts, or allays them, or risks what doubt he has, the risk is his. In terms of what his course will be, what he will or will not do or say, we are unpersuaded that he would distinguish between probably informers on the one hand and probable informers with transmitters on the other. ”