Opinion by
Mr. Justice Cohen,On August 27, 1963, at 2:45 p.m., two county detectives in plain clothes, armed with two search warrants and one arrest warrant, went to the home of defendant, a suspected bookmaker. As they approached the property, the detectives noticed defendant sitting at a window and observed him look in their direction. One of the detectives knocked on the door with his hand, waited about one minute during which time there was no response within, and knocked once again. Still hearing no response, the officers indicated that they were about to apply a crowbar between the door and jamb when the defendant cried out, “Don’t break my door. I will let you in.” Defendant then opened the door and admitted the detectives who identified them*86selves, read the warrants and began their search, in the course of which they confiscated two different editions of the Armstrong Daily and several blank sheets of paper. In addition, while the detectives were there, defendant received several telephone calls, all of which one of the officers answered, from parties seeking either to place bets or to learn the results of horse races.
At his trial on two indictments charging him with (1) setting up a gambling establishment and aiding and assisting others to gamble, and (2) bookmaking, defendant moved to suppress the evidence obtained in the search. This motion was dismissed and he was convicted of all charges. On appeal, the Superior Court affirmed judgment of sentence. We granted allocatur.
Defendant contends that the police officers failed to announce their identity and purpose prior to forcible entry, and that the resulting arrest and search and seizure were thereby rendered illegal. We do not agree.
In Mapp v. Ohio, 367 U.S. 643 (1961), the United States Supreme Court held that evidence obtained during an illegal search and seizure was not admissible in a state criminal proceeding. In Ker v. California, 374 U.S. 23 (1963), the Court held that the reasonableness of a state search was to be determined ultimately by the application of federal constitutional standards as expressed in the Fourth Amendment and the decisions of the Coui't applying that amendment. Yet, even in Ker, the Court recognized the right of the State to develop rules governing arrests and searches and seizures. Preserving this right in the state, Mr. Justice Clark stated: “We reiterate that the reasonableness of a search is in the first instance a substantive determination to be made by the trial court from the facts and circumstances of the case and in the light of the ‘fundamental criteria’ laid down by the Fourth Amendment and in opinions of this Court applying that Amendment. Findings of reasonableness, of course, are respected only *87insofar as consistent with federal constitutional guarantees. . . . The States are not thereby precluded from developing workable rules governing arrests, searches and seizures to meet ‘the practical demands of effective criminal investigation and law enforcement’ in the States, provided that those rules do not violate the constitutional proscription of unreasonable searches and seizures and the concomitant command that evidence so seized is inadmissible against one who has standing to complain. . . . Such a standard implies no derogation of uniformity in applying federal constitutional guarantees but is only a recognition that conditions and circumstances vary just as do investigative and enforcement techniques.” 374 U.S. at 33-34.
Such a recognition is especially pertinent to effective law enforcement against narcotics and gambling violations, where the possibility that evidence may be destroyed is particularly acute. Indeed, it is this very possibility which should allow state law enforcement officers to adopt techniques to suit the concrete situation. Blakey, The Rule of Announcement and Unlawful Entry: Miller v. United States and Ker v. California, 112 U. Pa. L. Rev. 499, 557 (1964). In view of the foregoing, the conduct of the county detectives in this matter did not violate the safeguards of the Fourth Amendment. The testimony reveals that they were observed by defendant as they approached his door; that there was an interval of silence which lasted one minute following their first knock at the door; and that even before they were able to apply the crowbar the defendant opened the door. Under these circumstances, it is obvious that defendant knew their identity and purpose without a formal announcement. Furthermore, there was absent here the “forceful entry” which confronted the Court in Ker. Although the argument may well be made that the detectives were not voluntarily admitted by defendant but gained admission by means *88of property duress, the entry was not unlawful under the Ker standard. Even the dissenters in Ker recognized that exceptions to the rule of announcement exist, inter alia, where the persons within already know of the officers’ authority and purpose or “where those within, made aware of the presence of someone outside (because, for example, there has been a knock at the door), are then engaged in activity which justifies the officers in the belief that an escape or the destruction of evidence is being attempted.” 374 U.S. at 47. Certainly, if the instant case does not fall within the former exception, then the lengthy silence maintained by defendant after observing the officers and hearing their knock would justify the application of the latter exception to the present matter. In any event, neither the arrest nor the search and seizure was violative of federal constitutional standards.
Defendant asserts that the instant matter is controlled by United States ex rel. Manduchi v. Tracy, 350 F. 2d 658 (3d Cir. 1965) by application of which his arrest, the search of his home and the seizure of evidence would all be violative of federal constitutional safeguards. In Manduchi, police officers, armed with a search warrant, broke down the accused’s door with a sledge hammer only a few seconds after knocking and receiving no response. At the same time, other officers broke through another door with a section of a telephone pole. The Third Circuit held that the search which followed was unreasonable and the evidence obtained therefrom inadmissible because the officers had not made known their identity and purpose, nor had they allowed the accused the opportunity of opening the door peacefully. Defendant herein has neither objection available to him, because he was given ample opportunity to open the door, as he finally did, and every indication was that he was well aware of who were at his door and why they were there.
*89Defendant further argues that the warrants carried by the officers were insufficient; that one of the detectives was improperly permitted to testify as an expert and express his opinion that defendant was a bookmaker; and that the evidence was insufficient to support the convictions. Each of these arguments is without merit and has been properly decided by the Superior Court.
Order of the Superior Court affirmed.
Mr. Justice Roberts concurs in the result and expresses no view with respect to the so-called “announcement” rule as the record in the instant case demonstrates that there was no “breaking” and, thus, no issue here presented under that rule.
Mr. Justice Eagen dissents.