Mr. Justice Jackson
delivered the opinion of the Court.
Petitioner was convicted on a two-count indictment, one charging the substantive offense of selling a pound of opium in violation of 21 U. S. C. §§ 173 and 174, the other conspiring to sell the opium in violation of 18 U. S. C. § 371. The Court of Appeals sustained the conviction by a divided court.1 We granted certiorari.2
The questions raised by petitioner have been considered but only one is of enough general interest to merit discussion. That concerns admission in evidence of two conversations petitioner had, while at large on bail pend[749]*749ing trial, with one Chin Poy. The circumstances are these:
Petitioner, On Lee, had a laundry in Hoboken. A customers’ room opened on the street, back of it was a room for ironing tables, and in the rear were his living quarters. Chin Poy, an old acquaintance and former employee, sauntered in and, while customers came and went, engaged the accused in conversation in the course of which petitioner made incriminating statements. He did not know that Chin Poy was what the Government calls “an undercover agent” and what petitioner calls a “stool pigeon” for the Bureau of Narcotics. Neither did he know that Chin Poy was wired for sound, with a small microphone in his inside overcoat pocket and a small antenna running along his arm. Unbeknownst to petitioner, an agent of the Narcotics Bureau named Lawrence Lee had stationed himself outside with a receiving set properly tuned to pick up any sounds the Chin Poy microphone transmitted. Through the large front window Chin Poy could be seen and through the receiving set his conversation, in Chinese, with petitioner could be heard by agent Lee. A few days later, on the sidewalks of New York, another conversation took place between the two, and damaging admissions were again “audited” by agent Lee.
Por reasons left to our imagination, Chin Poy was not called to testify about petitioner’s incriminating admissions. Against objection,3 however, agent Lee was al[750]*750lowed to relate the conversations as heard with aid of his receiving set. Of this testimony, it is enough to say that it was certainly prejudicial if its admission was improper.
Petitioner contends that this evidence should have been excluded because the manner in which it was ob[751]*751tained violates both the search-and-seizure provisions of the Fourth Amendment,4 and § 605 of the Federal Communications Act (47 U. S. C. § 605);5 and, if not rejected on those grounds, we should pronounce it inadmissible anyway under the judicial power to require fair play in federal law enforcement.
The conduct of Chin Poy and agent Lee did not amount to an unlawful search and seizure such as is proscribed by the Fourth Amendment. In Goldman v. United States, 316 U. S. 129, we held that the action of federal agents in placing a detectaphone on the outer wall of defendant’s hotel room, and thereby overhearing conversations held within the room, did not violate the Fourth Amendment. There the agents had earlier committed a trespass in order to install a listening device within the room itself. Since the device failed to work, the Court expressly reserved decision as to the effect on the search-and-seizure question of a trespass in that situation. Petitioner in the instant case has seized upon that dictum, apparently on the assumption that the presence of a radio set would automatically bring him within the reservation if he can show a trespass.
But petitioner cannot raise the undecided question, for here no trespass was committed. Chin Poy entered a place of business with the consent, if not by the implied [752]*752invitation, of the petitioner. Petitioner contends, however, that Chin Poy’s subsequent “unlawful conduct” vitiated the consent and rendered his entry a trespass ab initio.
If we were to assume that Chin Poy’s conduct was unlawful and consider this argument as an original proposition, it is doubtful that the niceties of tort law initiated almost two and a half centuries ago by the case of the Six Carpenters, 8 Coke 146 (a), cited by petitioner, are of much aid in determining rights under the Fourth Amendment. But petitioner’s argument comes a quarter of a century too late: this contention was decided adversely to him in McGuire v. United States, 273 U. S. 95, 98, 100, where Mr. Justice Stone, speaking for a unanimous Court, said of the doctrine of trespass ab initio: “This fiction, obviously invoked in support of a policy of penalizing the unauthorized acts of those who had entered under authority of law, has only been applied as a rule of liability in civil actions against them. Its extension is not favored.” He concluded that the Court would not resort to “a fiction whose origin, history, and purpose do not justify its application where the right of the government to make use of evidence is involved.” This was followed in Zap v. United States, 328 U. S. 624, 629.
By the same token, the claim that Chin Poy’s entrance was a trespass because consent to his entry was obtained by fraud must be rejected. Whether an entry such as this, without any affirmative misrepresentation, would be a trespass under orthodox tort law is not at all clear. See Prosser on Torts, § 18. But the rationale of the McGuire case rejects such fine-spun doctrines for exclusion of evidence. The further contention of petitioner that agent Lee, outside the laundry, was a trespasser because by these aids he overheard what went on inside verges on the frivolous. Only in the case of physical entry, either [753]*753by force, as in McDonald v. United States, 335 U. S. 451, by unwilling submission to authority, as in Johnson v. United States, 333 U. S. 10, or without any express or implied consent, as in Nueslein v. District of Columbia, 73 App. D. C. 85, 115 F. 2d 690, would the problem left undecided in the Goldman case be before the Court.
Petitioner relies on cases relating to the more common and clearly distinguishable problems raised where tangible property is unlawfully seized. Such unlawful seizure may violate the Fourth Amendment, even though the entry itself was by subterfuge or fraud rather than force. United States v. Jeffers, 342 U. S. 48; Gouled v. United States, 255 U. S. 298
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Mr. Justice Jackson
delivered the opinion of the Court.
Petitioner was convicted on a two-count indictment, one charging the substantive offense of selling a pound of opium in violation of 21 U. S. C. §§ 173 and 174, the other conspiring to sell the opium in violation of 18 U. S. C. § 371. The Court of Appeals sustained the conviction by a divided court.1 We granted certiorari.2
The questions raised by petitioner have been considered but only one is of enough general interest to merit discussion. That concerns admission in evidence of two conversations petitioner had, while at large on bail pend[749]*749ing trial, with one Chin Poy. The circumstances are these:
Petitioner, On Lee, had a laundry in Hoboken. A customers’ room opened on the street, back of it was a room for ironing tables, and in the rear were his living quarters. Chin Poy, an old acquaintance and former employee, sauntered in and, while customers came and went, engaged the accused in conversation in the course of which petitioner made incriminating statements. He did not know that Chin Poy was what the Government calls “an undercover agent” and what petitioner calls a “stool pigeon” for the Bureau of Narcotics. Neither did he know that Chin Poy was wired for sound, with a small microphone in his inside overcoat pocket and a small antenna running along his arm. Unbeknownst to petitioner, an agent of the Narcotics Bureau named Lawrence Lee had stationed himself outside with a receiving set properly tuned to pick up any sounds the Chin Poy microphone transmitted. Through the large front window Chin Poy could be seen and through the receiving set his conversation, in Chinese, with petitioner could be heard by agent Lee. A few days later, on the sidewalks of New York, another conversation took place between the two, and damaging admissions were again “audited” by agent Lee.
Por reasons left to our imagination, Chin Poy was not called to testify about petitioner’s incriminating admissions. Against objection,3 however, agent Lee was al[750]*750lowed to relate the conversations as heard with aid of his receiving set. Of this testimony, it is enough to say that it was certainly prejudicial if its admission was improper.
Petitioner contends that this evidence should have been excluded because the manner in which it was ob[751]*751tained violates both the search-and-seizure provisions of the Fourth Amendment,4 and § 605 of the Federal Communications Act (47 U. S. C. § 605);5 and, if not rejected on those grounds, we should pronounce it inadmissible anyway under the judicial power to require fair play in federal law enforcement.
The conduct of Chin Poy and agent Lee did not amount to an unlawful search and seizure such as is proscribed by the Fourth Amendment. In Goldman v. United States, 316 U. S. 129, we held that the action of federal agents in placing a detectaphone on the outer wall of defendant’s hotel room, and thereby overhearing conversations held within the room, did not violate the Fourth Amendment. There the agents had earlier committed a trespass in order to install a listening device within the room itself. Since the device failed to work, the Court expressly reserved decision as to the effect on the search-and-seizure question of a trespass in that situation. Petitioner in the instant case has seized upon that dictum, apparently on the assumption that the presence of a radio set would automatically bring him within the reservation if he can show a trespass.
But petitioner cannot raise the undecided question, for here no trespass was committed. Chin Poy entered a place of business with the consent, if not by the implied [752]*752invitation, of the petitioner. Petitioner contends, however, that Chin Poy’s subsequent “unlawful conduct” vitiated the consent and rendered his entry a trespass ab initio.
If we were to assume that Chin Poy’s conduct was unlawful and consider this argument as an original proposition, it is doubtful that the niceties of tort law initiated almost two and a half centuries ago by the case of the Six Carpenters, 8 Coke 146 (a), cited by petitioner, are of much aid in determining rights under the Fourth Amendment. But petitioner’s argument comes a quarter of a century too late: this contention was decided adversely to him in McGuire v. United States, 273 U. S. 95, 98, 100, where Mr. Justice Stone, speaking for a unanimous Court, said of the doctrine of trespass ab initio: “This fiction, obviously invoked in support of a policy of penalizing the unauthorized acts of those who had entered under authority of law, has only been applied as a rule of liability in civil actions against them. Its extension is not favored.” He concluded that the Court would not resort to “a fiction whose origin, history, and purpose do not justify its application where the right of the government to make use of evidence is involved.” This was followed in Zap v. United States, 328 U. S. 624, 629.
By the same token, the claim that Chin Poy’s entrance was a trespass because consent to his entry was obtained by fraud must be rejected. Whether an entry such as this, without any affirmative misrepresentation, would be a trespass under orthodox tort law is not at all clear. See Prosser on Torts, § 18. But the rationale of the McGuire case rejects such fine-spun doctrines for exclusion of evidence. The further contention of petitioner that agent Lee, outside the laundry, was a trespasser because by these aids he overheard what went on inside verges on the frivolous. Only in the case of physical entry, either [753]*753by force, as in McDonald v. United States, 335 U. S. 451, by unwilling submission to authority, as in Johnson v. United States, 333 U. S. 10, or without any express or implied consent, as in Nueslein v. District of Columbia, 73 App. D. C. 85, 115 F. 2d 690, would the problem left undecided in the Goldman case be before the Court.
Petitioner relies on cases relating to the more common and clearly distinguishable problems raised where tangible property is unlawfully seized. Such unlawful seizure may violate the Fourth Amendment, even though the entry itself was by subterfuge or fraud rather than force. United States v. Jeffers, 342 U. S. 48; Gouled v. United States, 255 U. S. 298 (the authority of the latter case is sharply limited by Olmstead v. United States, 277 U. S. 438, at 463). But such decisions are inapposite in the field of mechanical or electronic devices designed to overhear or intercept conversation, at least where access to the listening post was not obtained by illegal methods.
Petitioner urges that if his claim of unlawful search and seizure cannot be sustained on authority, we reconsider the question of Fourth Amendment rights in the field of overheard or intercepted conversations. This apparently is upon the theory that since there was a radio set involved, he could succeed if he could persuade' the Court to overturn the leading case holding wiretapping to be outside the ban of the Fourth Amendment, Olmstead v. United States, 277 U. S. 438, and the cases which have followed it. We need not consider this, however, for success in this attempt, which failed in Goldman v. United States, 316 U. S. 129, would be of no aid to petitioner unless he can show that his situation should be treated as wiretapping. The presence of a radio set is not sufficient to suggest more than the most attenuated analogy to wiretapping. Petitioner was talking confidentially and indiscreetly with one he trusted, and he [754]*754was overheard. This was due to aid from a transmitter and receiver, to be sure, but with the same effect on his privacy as if agent Lee had been eavesdropping outside an open window. The use of bifocals, field glasses or the telescope to magnify the object of a witness’ vision is not a forbidden search or seizure, even if they focus without his knowledge or consent upon what one supposes to be private indiscretions. 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.
Nor do the facts show a violation of § 605 of the Federal Communications Act. Petitioner had no wires and no wireless. There was no interference with any communications facility which he possessed or was entitled to use. He was not sending messages to anybody or using a system of communications within the Act. Goldstein v. United States, 316 U. S. 114.
Finally, petitioner contends that even though he be overruled in all else, the evidence should be excluded as a means of disciplining law enforcement officers. Cf. McNabb v. United States, 318 U. S. 332. In McNabb, however, we held that, where defendants had been unlawfully detained in violation of the federal statute requiring prompt arraignment before a commissioner, a confession made during the detention would be excluded as evidence in federal courts even though not inadmissible on the ground of any otherwise involuntary character. But here neither agent nor informer violated any federal law; and violation of state law, even had it been shown here, as it was not, would not render the evidence [755]*755obtained inadmissible in federal courts. Olmstead v. United States, 277 U. S. 438, at 468.
In order that constitutional or statutory rights may not be undermined, this Court has on occasion evolved or adopted from the practice of other courts exclusionary rules of evidence going beyond the requirements of the constitutional or statutory provision. McNabb v. United States, supra; Weeks v. United States, 232 U. S. 383. In so doing, it has, of course, departed from the common-law rule under which otherwise admissible evidence was not rendered inadmissible by the fact that it had been illegally obtained. Such departures from the primary evidentiary criteria of relevancy and trustworthiness must be justified by some strong social policy. In discussing the extension of such rules, and the creation of new ones, it is well to remember the remarks of Mr. Justice Stone in McGuire v. United States, 273 U. S. 95, at 99: “A criminal prosecution is more than a game in which the Government may be checkmated and the game lost merely because its officers have not played according to rule.”
Rules of evidence, except where prescribed by statute, are formulated by the courts to some extent, as “a question of sound policy in the administration of the law.” Zucker v. Whitridge, 205 N. Y. 50, 65, 98 N. E. 209, 213. Courts which deal with questions of evidence more frequently than we do have found it unwise to multiply occasions when the attention of a trial court in a criminal case must be diverted from the issue of the defendant’s guilt to the issue of someone else’s misconduct in obtaining evidence. They have considered that “The underlying principle obviously is that the court, when engaged in trying a criminal cause, will not take notice of the manner in which witnesses have possessed themselves of papers, or other articles of personal property, which [756]*756are material and properly offered in evidence.” People v. Adams, 176 N. Y. 351, 358, 68 N. E. 636, 638. However, there is a procedure in federal court by which defendant may protect his right in advance of trial to have returned to him evidence unconstitutionally obtained. Silverthorne Lumber Co. v. United States, 251 U. S. 385. But since we hold here that there was no violation of the Constitution, such a remedy could not be invoked. Exclusion would have to be based on a policy which placed the penalizing of Chin Poy’s breach of confidence above ordinary canons of relevancy. For On Lee’s statements to Chin Poy were admissions against interest provable against him as an exception to the hearsay rule. The normal manner of proof would be to call Chin Poy and have him relate the conversation. We can only speculate on the reasons why Chin Poy was not called. It seems a not unlikely assumption that the very defects of character and blemishes of record which made On'Lee trust him with confidences would make a jury distrust his testimony. Chin Poy was close enough to the underworld to serve as bait, near enough the criminal design so that petitioner would embrace him as a confidante, but too close to it for the Government to vouch for him as a witness. Instead, the Government called agent Lee. We should think a jury probably would find the testimony of agent Lee to have more probative value than the word of Chin Poy.
Society can ill afford to throw away the evidence produced by the falling out, jealousies, and quarrels of those who live by outwitting the law. Certainly no one would foreclose the turning of state’s evidence by denizens of the underworld. No good reason of public policy occurs to us why the Government should be deprived of the benefit of On Lee’s admissions because he made them to a confidante of shady character.
[757]*757The trend of the law in recent years has been to turn away from rigid rules of incompetence, in favor of admitting testimony and allowing the trier of fact to judge the weight to be given it. As this Court has pointed out: “ 'Indeed, the theory of the common law was to admit to the witness stand only those presumably honest, appreciating the sanctity of an oath, unaffected as a party by the result, and free from any of the temptations of interest. The courts were afraid to trust the intelligence of jurors. But the last fifty years have wrought a great change in these respects, and to-day the tendency is to enlarge the domain of competency and to submit to the jury for their consideration as to the credibility of the witness those matters which heretofore were ruled sufficient to justify his exclusion. This change has been wrought partially by legislation and partially by judicial construction.’ ” Funk v. United States, 290 U. S. 371, 376.
The use of informers, accessories, accomplices, false friends, or any of the other betrayals which are “dirty business” may raise serious questions of credibility. To the extent that they do, a defendant is entitled to broad latitude to probe credibility by cross-examination and to have the issues submitted to the jury with careful instructions. But to the extent that the argument for exclusion departs from such orthodox evidentiary canons as relevancy and credibility, it rests solely on the proposition that the Government shall be arbitrarily penalized for the low morals of its informers. However unwilling we as individuals may be to approve conduct such as that of Chin Poy, such disapproval must not be thought to justify a social policy of the magnitude necessary to arbitrarily exclude otherwise relevant evidence. We think the administration of justice is better served if stratagems such as we have here are regarded as raising, [758]*758not questions of law, but issues of credibility. We cannot say that testimony such as this shall, as a matter of law, be refused all hearing.
Judgment affirmed.
Mr. Justice Black
believes that in exercising its supervisory authority over criminal justice in the federal courts (see McNabb v. United States, 318 U. S. 332, 341) this Court should hold that the District Court should have rejected the evidence here challenged.