MOSK, J.
Defendants, charged with violation of three sections of the Health and Safety Code, moved unsuccessfully to set aside the information pursuant to Penal Code section 995, and failed to obtain a writ of prohibition in the Court of Appeal. We granted defendants' petition for hearing in order to decide whether a magistrate who issues a search warrant may relieve police officers of the statutory duty to give notice of their authority and purpose before entering a house to serve a warrant.
Defendants were charged in three separate counts with violating Health and Safety Code sections 11500.5, 11910 and 11555.
On March 17, 1972, officers of the Riverside Police Department executed a search warrant for a particular dwelling house. The warrant issued by the magistrate specifically provided that the officers "need not comply with Penal Code Section 1531." Upon arrival at the location, one of the officers crawled through a bedroom window which had no glass or screen but over which a cloth had been tied down to exclude both light and the elements. The officer, before entering, gave no notice of his authority or purpose. The subsequent search of the dwelling yielded various articles which appeared to the officers to be narcotics and which defendants now concede to be contraband. Defendants, who were occupants of the building, were both arrested.
Entry through such an aperture constitutes a breaking within the meaning of section 1531. ( People v. Rosales (1968) 68 Cal.2d 299, 303 [ 66 Cal.Rptr. 1, 437 P.2d 489].)
Once inside the dwelling, the officer informed defendant Parsley, "We're police officers." This statement does not satisfy section 1531 because (1) it was made inside the house, and (2) it did not include a statement of purpose.
(1,2) Penal Code section 1531 provides: "The officer may break open any outer or inner door or window of a house, or any part of a house or anything therein, to execute the warrant, if, after notice of his authority and purpose, he is refused admittance." An equivalent provision, Penal Code section 844, governs entry without a warrant to effect an arrest. (See People v. Gastelo (1967) 67 Cal.2d 586, 588 [ 63 Cal.Rptr. 10, 432 P.2d 706].) The negative inference flowing from these provisions serves to bar most unannounced entries and to render inadmissible evidence seized pursuant thereto. ( Greven v. Superior Court (1969) 71 Cal.2d 287, 295 [ 78 Cal.Rptr. 504, 455 P.2d 432]; People v. Maddox (1956) 46 Cal.2d 301, 305-307 [ 294 P.2d 6].) We have held, however, that failure to comply with sections 1531 and 844 does not compel application of the exclusionary rule "if the specific facts known to the officer before his entry are sufficient to support his good faith belief that compliance will increase his peril, frustrate the arrest, or permit the destruction of evidence." ( People v. Tribble (1971) 4 Cal.3d 826, 833 [ 94 Cal.Rptr. 613, 484 P.2d 589]; People v. Gastelo (1967) supra, 67 Cal.2d 586, 587-588; People v. Maddox (1956) supra, 46 Cal.2d 301, 306.)
We hold the superior court erred in concluding advance judicial approval may excuse compliance with statutory announcement requirements.
Sections 1531 and 844 are striking in that the Legislature failed to include in either statute any exceptions to the rule that an officer must provide notice of his authority and purpose and seek consent to admittance before resorting to forcible entry. (3, 4) We have construed the statutes to contain implicit exceptions for articulated exigent circumstances on the ground that "since the demand and explanation requirements . . . are a codification of the common law, they may reasonably be interpreted as limited by the common law rules. . . ." ( People v. Maddox (1956) supra, 46 Cal.2d 1, 306.)
These common law exceptions pertain only to emergency situations existing at the time of entry. There appears to be no common law doctrine empowering courts to authorize in advance noncompliance with announcement requirements. Thus, the ground which supports excusal of compliance after the fact of entry cannot be extended to validate prior judicial authorization. This consideration appears to underlie our provision in Maddox that the existence of exigent circumstances must be determined "[w]ithout the benefit of hindsight and ordinarily on the spur of the moment, [and] the officer must decide these questions in the first instance." (Italics added.) (46 Cal.2d at p. 306.)
Further, evidence that the Legislature intended to preclude warrants authorizing in advance noncompliance with announcement requirements appears from a comparison of section 1531 with section 1533, which concerns nighttime entry. Section 1533 provides: "Upon a showing of good cause, the magistrate may, in his discretion, insert a direction in a search warrant that it may be served at any time of the day or night. In the absence of such a direction, the warrant shall be served only between the hours of 7 o'clock a.m. and 10 o'clock p.m." The fact that this section expressly provides for prior judicial authorization while section 1531 fails to do so clearly implies, under the doctrine of inclusio unius est exclusio alterius, that the Legislature intended not to permit warrants to excuse unannounced entry.
Inasmuch as the Legislature has provided no authority for inserting directions in warrants excusing compliance with statutory announcement requirements and has in fact impliedly barred such a procedure, the courts are without power to institute a practice of issuing such warrants unless prior judicial authorization of noncompliance is constitutionally mandated. We conclude that it is not.
(5) While the requirements of announcement before entry have been held to be compelled by the guarantees against search and seizure contained in the Fourth Amendment ( Ker v. California (1963) 374 U.S. 23 [10 L.Ed.2d 726, 83 S.Ct. 1623]; People v. Gastelo (1967) supra, 67 Cal.2d 586, 588-589), police officers have no constitutional duty to obtain prior judicial authorization to enter without notice. The proposition that searches without a warrant are unreasonable per se except in a few narrowly defined circumstances does not apply to the issue of unannounced entry. The reason for this distinction is that information providing probable cause for the issuance of a search warrant is of a different nature and source than information justifying unannounced entry. While a search warrant must necessarily rest upon previously obtained information, unannounced entry is excused only on the basis of exigent circumstances existing at the time an officer approaches a site to make an arrest or execute a warrant. Facts existing at the time of obtaining a warrant may no longer exist at the time of entry. Such an emergency, therefore, can be judged only in light of circumstances of which the officer is aware at the latter moment. Previously obtained information may at that time be taken into account in determining the necessity of dispensing with ordinary announcements ( People v. Dumas (1973) ante, pp. 871, 877-879 [ 109 Cal.Rptr. 304, 512 P.2d 1208]), but a more significant factor in this decision is perception and knowledge the officer acquires on the scene immediately prior to effecting entry. For this reason, earlier judicial authorization would be largely inappropriate in the context of unannounced entry and, thus, clearly cannot be considered a constitutional requirement.
Statistical data submitted to us indicate the increased use of warrants providing advance excusal of compliance with statutory announcement requirements. For the year April 1, 1972, to March 31, 1973, 12 percent of all search warrants issued in Los Angeles County contained such a provision, a figure that suggests requests are not limited to true prospective emergency circumstances. Were we to approve this practice, there would be an understandable temptation for agencies to use pre-prepared request forms and to seek exemption in most cases. This would, for all practical purposes, eliminate sections 1531 and 844 from the statute books and judicially legislate in their place a de facto no-knock rule.
(6) We conclude, for all the foregoing reasons, that the magistrate was without power to give prior authorization for violation of section 1531 and that the People may not rely on such advance excusal to justify the officers' failure to comply with that section in the present case. As discussed above, the key to permissible unannounced entry is the knowledge of exigent circumstances possessed by police officers at the time of entry. Thus, from the viewpoint of a court reviewing justification for an unannounced entry after the fact, a warrant authorizing such action adds nothing.
At defendants' preliminary hearing the judge upheld the unannounced entry into their residence solely on the basis of the purported authority to effect such entry contained in the warrant. This was error. The People contend, however, the error was harmless in that sufficient evidence was introduced at the preliminary hearing to demonstrate that the police officers who effected the unannounced entry were in fact acting in response to what they perceived to be a demonstrable emergency.
The People introduced evidence at the preliminary hearing, including the averments contained in the warrant affidavit, that police officers had, through a confidential informant, made controlled purchases of narcotics from an individual inside defendants' residence. The informant assertedly told the officers he had seen a shotgun in the possession of this individual and that the individual was "known to" answer the door while armed with this weapon. According to the warrant affidavit, similar information had reached the police officers from "numerous other persons acquainted with the suspect."
(7) While knowledge that a person in a house to be entered is "known to" answer the door armed with a firearm might be sufficient, under some circumstances, to excuse police officers from announcement requirements (cf. People v. Dumas, supra, ante, pp. 871, 878-879), we hold that the evidence suggesting the officers in this case possessed such knowledge was incompetent and thus inadmissible at the preliminary hearing.
At that hearing defendants' counsel objected to introduction of evidence of information received from the confidential informant and repeatedly moved for disclosure of the informant's identity. The objection was overruled and the motions denied. The facts of this case are similar to Priestly v. Superior Court (1958) 50 Cal.2d 812 [ 330 P.2d 39]. In that case the prosecution at the preliminary hearing sought to show reasonable cause for a warrantless search by testimony as to communications from a confidential informant. The defendant sought unsuccessfully to exclude that testimony or to compel disclosure of the informant's identity. We held that the information must be set aside, stating: "If testimony of communications from a confidential informer is necessary to establish the legality of a search, the defendant must be given a fair opportunity to rebut that testimony. He must therefore be permitted to ascertain the identity of the informer, since the legality of the officer's actions depends upon the credibility of the information, not upon facts that he directly witnessed and upon which he could be cross-examined." (50 Cal.2d at p. 818.) The testimony as to evidence received from the confidential informant was, therefore, held incompetent to support the validity of the search.
The rule in Priestly was modified by the enactment of Evidence Code section 1042, subdivision (c), which provides: "[I]n any preliminary hearing, criminal trial, or other criminal proceeding, any otherwise admissible evidence of information communicated to a peace officer by a confidential informant, who is not a material witness to the guilt or innocence of the accused of the offense charged, is admissible on the issue of reasonable cause to make an arrest or search without requiring that the name or identity of the informant be disclosed if the judge or magistrate is satisfied, based upon evidence produced in open court, out of the presence of the jury, that such information was received from a reliable informant and in his discretion does not require such disclosure."
This section appears to include issues of reasonableness of unannounced entry within the language "reasonable cause to make an arrest or search." Under this section, in order to admit at a preliminary hearing evidence relevant to the reasonableness of an arrest or search that is based on communications of a confidential informant, the judge or magistrate must either (1) compel disclosure of the informant's identity as required by Priestly, or (2) exercise his discretion based on evidence produced in open court that the informant is reliable and that disclosure is not required.
The judge at the preliminary hearing in the present case followed neither course. In ruling that the unannounced entry was justified by the warrant provision alone, he avoided the requirement of disclosing the informant's identity (Evid. Code, § 1042, subd. (b)), but did so without exercising his discretion as to the informant's reliability based on evidence produced in open court. The judge, moreover, restricted cross-examination of the testifying police officers by defendants' counsel concerning the reliability of the informant's communications on the ground that the warrant was sufficient on its face to authorize the unannounced entry. One of the officers, for example, was prevented by the judge from answering the preliminary question, "Just what did [the informant] say?"
(8) Full cross-examination of prosecution witnesses concerning informant reliability is not only necessary for a proper exercise of the court's discretion on this issue under section 1042, subdivision (c), it appears to be a constitutional prerequisite to invoking the informant privilege. In McCray v. Illinois (1967) 386 U.S. 300 [18 L.Ed.2d 62, 87 S.Ct. 1056], the United States Supreme Court held that the Constitution does not require abolition of the informant privilege where the communication from the informant has been used merely to establish cause for an arrest or search. In upholding the privilege, however, the court emphasized the procedures that had been followed to determine the informant's reliability: "The arresting officers in this case testified, in open court, fully and in precise detail as to what the informer told them and as to why they had reason to believe his information was trustworthy. Each officer was under oath. Each was subjected to searching cross-examination. The judge was obviously satisfied that each was telling the truth, and for that reason he exercised the discretion conferred upon him by the established law of Illinois to respect the informer's privilege." ( Id. at p. 313 [18 L.Ed.2d at p. 72].)
In contrast to that procedure, the judge's failure to allow cross-examination and to exercise his statutory discretion at the preliminary hearing in the instant case renders incompetent the evidence concerning communications from the confidential informant. (9) That evidence provides the only possible excuse for the unannounced entry into defendants' residence. Consequently, the inculpatory evidence discovered in the subsequent search, which was the sole basis for the filing of the information, is likewise incompetent. Inasmuch as defendants were thus committed where there was no competent evidence to show they were guilty of a public offense, the information must be set aside under Penal Code section 995. ( Priestly v. Superior Court (1958) supra, 50 Cal.2d 812, 815.)
Let the peremptory writ of prohibition issue as prayed.
Wright, C.J., Tobriner, J., and Sullivan, J., concurred.