opinion: Mr. Justice White
  announced the judgment of the Court and an opinion in which The Chief Justice, Mr. Justice Stewart, and Mr. Justice Blackmun join.
  In 1966, respondent James A. White was tried and convicted under two consolidated indictments charging various illegal transactions in narcotics violative of 26 U. S. C. § 4705 (a) and 21 U. S. C. § 174. He was fined and sentenced as a second offender to 25-year concurrent sentences. 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. On four occasions the conversations took place in Jackson’s home; each of these conversations was overheard by an agent concealed in a kitchen closet with Jackson’s consent and by a second agent outside the house using a radio receiver. Four other conversations — one in respondent’s home, one in a restaurant, and two in Jackson’s car — were overheard by the use of radio equipment. The prosecution was unable to locate and produce Jackson at the trial and the trial court overruled objections to the testimony of the agents who conducted the electronic surveillance. The jury returned a guilty verdict and defendant appealed.
  The Court of Appeals read Katz v. United States, 389 U. S. 347 (1967), as overruling On Lee v. United States, 343 U. S. 747 (1952), and interpreting the Fourth Amendment to forbid the introduction of the agents’ testimony in the circumstances of this case. Accordingly, the court reversed but without adverting to the fact that the transactions at issue here had occurred before Katz was decided in this Court. In our view, the Court of Appeals misinterpreted both the Katz case and the Fourth Amendment and in any event erred in applying the Katz case to events that occurred before that decision was rendered by this Court.
  I
  Until Katz v. United States, neither wiretapping nor electronic eavesdropping violated a defendant's Fourth Amendment rights “unless there has been an official search and seizure of his person, or such a seizure of his papers or his tangible material effects, or an actual physical invasion of his house 'or curtilage’ for the purpose of making a seizure.” Olmstead v. United States, 277 U. S. 438, 466 (1928); Goldman v. United States, 316 U. S. 129, 135-136 (1942). But where “eavesdropping was accomplished by means of an unauthorized physical penetration into the premises occupied” by the defendant, although falling short of a “technical trespass under the local property law,” the Fourth Amendment was violated and any evidence of what was seen and heard, as well as tangible objects seized, was considered the inadmissible fruit of an unlawful invasion. Silverman v. United States, 365 U. S. 505, 509, 511 (1961); see also Wong Sun v. United States, 371 U. S. 471 (1963); Berger v. New York, 388 U. S. 41, 52 (1967); Alderman v. United States, 394 U. S. 165, 177-178 (1969).
  Katz v. United States, however, finally swept away doctrines that electronic eavesdropping is permissible under the Fourth Amendment unless physical invasion of a constitutionally protected area produced the challenged evidence. In that case government agents, without petitioner’s consent or knowledge, attached a listening device to the outside of a public telephone booth and recorded the defendant’s end of his telephone conversations. In declaring the recordings inadmissible in evidence in the absence of a warrant authorizing the surveillance, the Court overruled Olmstead and Goldman and held that the absence of physical intrusion into the telephone booth did not-justify using electronic devices in listening to and recording Katz’ words, thereby violating the privacy on which he justifiably relied while using the telephone in those circumstances.
  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.
  Hoffa v. United States, 385 U. S. 293 (1966), which was left undisturbed by Katz, held that however strongly a defendant may trust an apparent colleague, his expectations in this respect are not protected by the Fourth Amendment when it turns out that the colleague is a government agent regularly communicating with the authorities. In these circumstances, “no interest legitimately protected by the Fourth Amendment is involved,” for that amendment affords no protection to “a wrongdoer’s misplaced belief that a person to whom he voluntarily confides his wrongdoing will not reveal it.” Hoffa v. United States, at 302. No warrant to “search and seize” is required in such circumstances, nor is it when the Government sends to defendant’s home a secret agent who conceals his identity and makes a purchase of narcotics from the accused, Lewis v. United States, 385 U. S. 206 (1966), or when the same agent, unbeknown to the defendant, carries electronic equipment to record the defendant’s words and the evidence so gathered is later offered in evidence. Lopez v. United States, 373 U. S. 427 (1963).
  Conceding that Hoffa, Lewis, and Lopez remained unaffected by Katz, the Court of Appeals nevertheless read both Katz and the Fourth Amendment to require a different result if the agent not only records his conversations with the defendant but instantaneously transmits them electronically to other agents equipped with radio receivers. Where this occurs, the Court of Appeals held, the Fourth Amendment is violated and the testimony of the listening agents must be excluded from evidence.
  To reach this result it was necessary for the Court of Appeals to hold that On Lee v. United States was no longer good law. In that case, which involved facts very similar to the case before us, the Court first rejected claims of a Fourth Amendment violation because the informer had not trespassed when he entered the defendant's premises and conversed with him. To this extent the Court’s rationale cannot survive Katz. See 389 U. S., at 352-353. But the Court announced a second and independent ground for its decision; for it went on to say that overruling Olmstead and Goldman would be of no aid to On Lee since he “was talking confidentially and indiscreetly with one he trusted, and he was overheard. ... It would be a dubious service to the genuine liberties protected by the Fourth Amendment to make them bedfellows with spurious liberties improvised by farfetched analogies which would liken eavesdropping on a conversation, with the connivance of one of the parties, to an unreasonable search or seizure. We find no violation of the Fourth Amendment here.” 343 U. S., at 753-754. We see no indication in Katz that the Court meant to disturb that understanding of the Fourth Amendment or to disturb the result reached in the On Lee case, nor are we now inclined to overturn this view of the Fourth Amendment.
  Concededly a police agent who conceals his police connections may write down for official use his conversations with a defendant and testify concerning them, without a warrant authorizing his encounters with the defendant and without otherwise violating the latter’s Fourth Amendment rights. Hoffa v. United States, 385 U. S., at 300-303. For constitutional purposes, no' different result is required if the agent instead of immediately reporting and transcribing his conversations with defendant, either (1) simultaneously records them with electronic equipment which he is carrying on his person, Lopez v. United States, supra; (2) or carries radio equipment which simultaneously transmits the conversations either to recording equipment located elsewhere or to other agents monitoring the transmitting frequency. On Lee v. United States, supra. If the conduct and revelations of an agent operating without electronic equipment do not invade the defendant’s constitutionally justifiable expectations of privacy, neither does a simultaneous recording of the same conversations made by the agent or by others from transmissions received from the agent to whom the defendant is talking and whose trustworthiness the defendant necessarily risks.
  Our problem is not what the privacy expectations of particular defendants in particular situations may be or the extent to which they may in fact have relied on the discretion of their companions. Very probably, individual defendants neither know nor suspect that their colleagues have gone or will go to the police or are carrying recorders or transmitters. Otherwise, conversation would cease and our problem with these encounters would be nonexistent or far different from those now before us. Our problem, in terms of the principles announced in Katz, is what expectations of privacy are constitutionally “justifiable”' — what expectations the Fourth Amendment will protect in the absence of a warrant. So far, the law permits the frustration of actual expectations of privacy by permitting authorities to use the testimony of those associates who for one reason or another have determined to turn to the police, as well as by authorizing the use of informants in the manner exemplified by Hoff a and Lewis. If the law gives no protection to the wrongdoer whose trusted accomplice is or becomes a police agent, neither should it protect him when that same agent has recorded or transmitted the conversations which are later offered in evidence to prove the State’s case. See Lopez v. United States, 373 U. S. 427 (1963).
  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 probable informers on the one hand and probable informers with transmitters on the other. Given the possibility or probability that one of his colleagues is cooperating with the police, it is only speculation to assert that the defendant’s utterances would be substantially different or his sense of security any less if he also thought it possible that the suspected colleague is wired for sound. At least there is no persuasive evidence that the difference in this respect between the electronically equipped and the unequipped agent is substantial enough to require discrete constitutional recog-ration, particularly under the Fourth Amendment which is ruled by fluid concepts of “reasonableness.”
  Nor should we be too ready to erect constitutional barriers to relevant and probative evidence which is also accurate and reliable. An electronic recording will many times produce a more reliable rendition of what a defendant has said than will the unaided memory of a police agent. 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.
  It is thus untenable to consider the activities and reports of the police agent himself, though acting without a warrant, to be a “reasonable” investigative effort and lawful under the Fourth Amendment but to view the same agent with a recorder or transmitter as conducting an “unreasonable” and unconstitutional search and seizure. Our opinion is currently shared by Congress and the Executive Branch, Title III, Omnibus Crime Control and Safe Streets Act of 1968, 82 Stat. 212, 18 U. S. C. §2510 et seq. (1964 ed., Supp. V), and the American Bar Association. Project on Standards for Criminal Justice, Electronic Surveillance § 4.1 (Approved Draft 1971). It is also the result reached by prior cases in this Court. On Lee, supra; Lopez v. United States, supra.
  No different result should obtain where, as in On Lee and the instant case, the informer disappears and is unavailable at trial; for the issue of whether specified events on a certain day violate the Fourth Amendment should not be determined by what later happens to the informer. His unavailability at trial and proffering the testimony of other agents may raise evidentiary problems or pose issues of prosecutorial misconduct with respect to the informer’s disappearance, but they do not appear critical to deciding whether prior events invaded the defendant’s Fourth Amendment rights.
  II
  The Court of Appeals was in error for another reason. In Desist v. United States, 394 U. S. 244 (1969), we held that our decision in Katz v. United States applied only to those electronic surveillances that occurred subsequent to the date of that decision. Here the events in question took place in late 1965 and early 1966, long prior to Katz. We adhere to the rationale of Desist, see Williams v. United States, ante, p. 646. It was error for the Court of Appeals to dispose of this case based on its understanding of the principles announced in the Katz case. The court should have judged this case by the pr e-Katz law and under that law, as On Lee clearly holds, the electronic surveillance here involved did not violate White’s rights to be free from unreasonable searches and seizures.
  The judgment of the Court of Appeals is reversed.
  It is so ordered.
  Mr. Justice Black, while adhering to his views expressed in Linkletter v. Walker, 381 U. S. 618, 640 (1965), concurs in the judgment of the Court for the reasons set forth in his dissent in Katz v. United States, 389 U. S. 347, 364 (1967).
  White argues that Jackson, though admittedly “cognizant” of the presence of transmitting devices on his person, did not voluntarily consent thereto. Because the court below did not reach the issue of Jackson’s consent, we decline to do so. Similarly, we do not consider White’s claim that the Government’s actions violated state law.
  A panel of three judges on March 18, 1968, reversed the conviction, one judge dissenting. A rehearing en banc was granted, and on January 7, 1969, the full court followed the panel’s decision, three judges dissenting. 405 F. 2d 838.
  It follows from our opinion that we reject respondent’s contentions that Lopez should be overruled.
  Other courts of appeals have considered On Lee viable despite Katz. Dancy v. United States, 390 F. 2d 370 (CA5 1968); Long v. United States, 387 F. 2d 377 (CA5 1967); Koran v. United States, 408 F. 2d 1321 (CA5 1969). See also United States v. Kaufer, 406 F. 2d 550 (CA2), aff’d per curiam, 394 U. S. 458 (1969); United States v. Jackson, 390 F. 2d 317 (CA2 1968); Doty v. United States, 416 F. 2d 887 (CA10 1968), id., at 893 (rehearing 1969).