opinion: Justice Ginsburg
  delivered the opinion of the Court.
  The question presented in this case is whether an anonymous tip that a person is carrying a gun is, without more, sufficient to justify a police officer’s stop and frisk of that person. We hold that it is not.
  I
  On October 13, 1995, an anonymous caller reported to the Miami-Dade Police that a young black male standing at a particular bus stop and wearing a plaid shirt was carrying a gun. App. to Pet. for Cert. A-40 to A-41. So far as the record reveals, there is no audio recording of the tip, and nothing is known about the informant. Sometime after the police received the tip — the record does not say how long— two officers were instructed to respond. They arrived at the bus stop about six minutes later and saw three black males “just hanging out [there].” Id., at A-42. One of the three, respondent J. L., was wearing a plaid shirt. Id., at A-41. Apart from the tip, the officers had.no reason tp suspect any of the three of illegal conduct. The officers did not see a firearm, and J. L. made no threatening or otherwise unusual movements. Id., at A-42 to A-44. One of the officers approached J. L., told him to put his hands up on the bus stop, frisked him, and seized a gun from J. L.’s pocket. The second officer frisked the other two individuals, against whom no allegations had been made, and found nothing.
  J. L., who was at the time of the frisk “10 days shy of his 16th birth[dayj,” Tr. of Oral Arg. 6, was charged under state law with carrying a concealed firearm without a license and possessing a firearm while under the age of 18. He moved to suppress the gun as the fruit of an unlawful search, and the trial court granted his motion. The intermediate appellate court reversed, but the Supreme Court of Florida quashed that decision and held the search invalid under the Fourth Amendment. 727 So. 2d 204 (1998).
  Anonymous tips, the Florida Supreme Court stated, are generally less reliable than tips from known informants and can form the basis for reasonable suspicion only'if accompanied by specific indicia of reliability, for example, the correct forecast of a subject’s “‘not easily predicted’” movements. Id., at 207 (quoting Alabama v. White, 496 U. S. 325, 332 (1990)), The tip leading to the frisk of J. L., the court observed, provided no such predictions, nor did it contain any other qualifying indicia of reliability. 727 So. 2d, at 207-208. Two justices dissented. The safety of the police and the public, they maintained, justifies a “firearm exception” to the general rule barring investigatory stops and frisks on the basis of bare-boned anonymous tips. Id., at 214-215.
  Seeking review in this Court, the State of Florida noted that the decision of the State’s Supreme Court conflicts with decisions of other courts declaring similar searches compatible with the Fourth Amendment. See, e. g., United States v. DeBerry, 76 F. 3d 884, 886-887 (CA7 1996); United States v. Clipper, 973 F. 2d 944, 951 (CADC 1992). We granted certiorari, 528 U. S. 963 (1999), and now affirm the judgment of the Florida Supreme Court.
  HH
  Our stop and frisk” decisions begin with Terry v. Ohio, 392 U. S. 1 (1968). This Court held in Terry:
  “[Wjhere a police officer observes unusual conduct which leads him reasonably to conclude in light of his experience that criminal activity may be afoot and that the persons with whom he is dealing may be armed and presently dangerous, where in the course of investigating this behavior he identifies himself as a policeman and makes reasonable inquiries, and where nothing in the initial stages of the encounter serves to dispel his reasonable fear for his own or others’ safety, he is entitled for the protection of himself and others in the area to conduct a carefully limited search of the outer clothing of such persons in an attempt to discover weapons which might be used to assault him.” Id., at 30.
  In the instant case, the officers’ suspicion that J. L. was carrying a weapon arose not from any observations of their own but solely from a call made from an unknown location by an unknown caller. Unlike a tip from a known informant whose reputation can be assessed and who can be held responsible if her allegations turn out to be fabricated, see Adams v. Williams, 407 U. S. 143, 146-147 (1972), “an anonymous tip alone seldom demonstrates the informant’s basis of knowledge or veracity,” Alabama v. White, 496 U. S., at 329. As we have recognized, however, there are situations in which an anonymous tip, suitably corroborated, exhibits “sufficient indicia of reliability to provide reasonable suspicion to make the investigatory stop.” Id., at 327. The question we here confront is whether the tip pointing to J. L. had those indicia of reliability.
  In White, the police received an anonymous tip asserting that a woman was carrying cocaine and predicting that she would leave an apartment building at a specified time, get into a car matching a particular description, and drive to a named motel. Ibid. Standing alone, the tip would not have justified a Terry stop. 496 U. S., at 329. Only after police observation showed that the informant had accurately predicted the woman’s movements, we explained, did it become reasonable to think the tipster had inside knowledge about the suspect and therefore to credit his assertion about the cocaine. Id, at 332. Although the Court held that the suspicion in White became reasonable after police surveillance, we regarded the ease as borderline. Knowledge about a person’s future movements indicates some familiarity with that person’s affairs, but having such knowledge does not necessarily imply that the informant knows, in particular, whether that person is carrying hidden contraband. We accordingly classified White as a “close case.” Ibid.
  The tip in the instant case lacked the moderate indicia of reliability present in White and essential to the Court’s decision in that case. The anonymous call concerning J. L. provided no predictive information and therefore left the police without means to test the informant’s knowledge or credibility. That the allegation about the gun turned out to be correct does not suggest that the officers, prior to the frisks, had a reasonable basis for suspecting J. L. of engaging in unlawful conduct: The reasonableness of official suspicion must be measured by what the officers knew before they conducted their search. All the police had to go on in this case was the bare report of an unknown, unaccountable informant who neither explained how he knew about the gun nor supplied any basis for believing he had inside information about J. L. If White was a close case on the reliability of anonymous tips, this one surely falls on the other side of the line.
  Florida contends that the tip was reliable because its description of the suspect’s visible attributes proved accurate: There really was a young black male wearing a plaid shirt at the bus stop. Brief for Petitioner 20-21. The United States as amicus curiae makes a similar argument, proposing that a stop and frisk should be permitted “when (1) an anonymous tip provides a description of a particular person at a particular location illegally carrying a concealed firearm, (2) police promptly verify the pertinent details of the tip except the existence of the firearm, and (3) there are no factors that cast doubt on the reliability of the tip ... Brief for United States 16. These contentions misapprehend the reliability needed for a tip to justify a Terry stop.
  An accurate description of a subject’s readily observable location and appearance is of course reliable in this limited sense: It will help the police correctly identify the person whom the tipster means to accuse. Such a tip, however, does not show that the tipster has knowledge of concealed criminal activity. The reasonable suspicion here at issue requires that a tip be reliable in its assertion of illegality, not just in its tendency to identify a determinate person. Cf. 4 W. LaFave, Search and Seizure § 9.4(h), p. 213 (3d ed. 1996) (distinguishing reliability as to identification, which is often important in other criminal law contexts, from reliability as to the likelihood of criminal activity, which is central in anonymous-tip cases).
  A second major argument advanced by Florida and the United States as amicus is, in essence, that the standard Terry analysis should be modified to license a “firearm exception.” Under such an exception, a tip alleging an illegal gun would justify a stop and frisk even if the accusation would fail standard pre-search reliability testing. We decline to adopt this position.
  Firearms are dangerous, and extraordinary dangers sometimes justify unusual precautions. Our decisions recognize the serious threat that armed criminals pose to public safety; Terry’s rule, which permits protective police searches on the basis of reasonable suspicion rather than demanding that officers meet the higher standard of probable cause, responds to this very concern. See 392 U. S., at 30. But an automatic firearm exception to our established reliability analysis would rove too far. Such an exception would enable any person seeking to harass another to set in motion an intrusive, embarrassing police search of the targeted person simply by placing an anonymous call falsely reporting the target’s unlawful carriage of a gun. Nor could one securely confine such an exception to allegations involving firearms.
  Several Courts of Appeals have held it per se foreseeable for people carrying significant amounts of illegal drugs to be carrying guns as well. See, e. g., United States v. Sakyi, 160 F. 3d 164, 169 (CA4 1998); United States v. Dean, 59 F. 3d 1479, 1490, n. 20 (CA5 1995); United States v. Odom, 13 F. 3d 949, 959 (CA6 1994); United States v. Martinez, 958 F. 2d 217, 219 (CA8 1992). If police officers may properly conduct Terry frisks on the basis of bare-boned tips about guns, it would be reasonable to maintain under the above-cited decisions that the police should similarly have discretion to frisk based on bare-boned tips about narcotics. As we clarified when we made indicia of reliability critical in Adams and White, the Fourth Amendment is not so easily satisfied. Cf. Richards v. Wisconsin, 520 U. S. 385, 393-394 (1997) (rejecting a per se exception to the “knock and announce” rule for narcotics cases partly because “the reasons for creating an exception in one category [of Fourth Amendment eases] can, relatively easily, be applied to others,” thus allowing the exception to swallow the rule).
  The facts of this case do not require us to speculate about the circumstances under which the danger alleged in an anonymous tip might be so great as to justify a search even without a showing of reliability. We do not say, for example, that a report of a person carrying a bomb need bear the indicia of reliability we demand for a report of a person carrying a firearm before the police can constitutionally conduct a frisk. Nor do we hold that public safety officials in quarters where the reasonable expectation of Fourth Amendment privacy is diminished, such as airports, see Florida v. Rodriguez, 469 U. S. 1 (1984) (per curiam), and schools, see New Jersey v. T L. O., 469 U. S. 325 (1985), cannot conduct protective searches on the basis of information insufficient to justify searches elsewhere.
  Finally, the requirement that an anonymous tip bear standard indicia of reliability in order to justify a stop in no way diminishes a police officer’s prerogative, in accord with Terry, to conduct a protective search of a person who has already been legitimately stopped. We speak in today’s decision only of cases in which the officer’s authority to make the initial stop is at issue. In that context, we hold that an anonymous tip lacking indicia of reliability of the kind contemplated in Adams and White does not justify a stop and frisk whenever and however it alleges the illegal possession of a firearm.
  The judgment of the Florida Supreme Court is affirmed.
  It is so ordered.
  At oral argument, petitioner also advanced the position that J. L.’s youth made the stop and frisk valid, because it is a crime in Florida for persons under the age of 21 to carry concealed firearms. See Fla. Stat. § 790.01 (1997) (carrying a concealed weapon without a license is a misdemeanor), § 79Q.06(2)(b) (only persons aged 21 or older may be licensed to carry concealed weapons). This contention misses the mark. Even assuming that the arresting officers could be sure that J. L. was under 21, they would have had reasonable suspicion that J. L. was engaged in criminal activity only if they could be confident that he was carrying a gun in the first place. The mere fact that a tip, if true, would describe illegal activity does not mean that the police may make a Terry stop without meeting the reliability requirement, and the fact that J. L. was under 21 in no way made the gun tip more reliable than if he had been an adult.