Raymond Freitas was charged with possession of a controlled substance with intent to manufacture and to distribute and with conspiracy to manufacture in violation of 21 U.S.C. §§ 841 (a)(1) and 846. The government appeals from the district court’s order suppressing evidence of drug-related activity, 610 F.Supp. 1560 . We reverse the district court and remand for further proceedings consistent with this opinion.

I.

FACTS AND PROCEEDINGS BELOW

On July 27, 1984, an anonymous informant telephoned the Drug Enforcement Agency (DEA) and indicated that Raymond Freitas was running a methamphetamine laboratory at his home in Clearlake, California. Sometime in mid-August, the same informant told the DEA that Freitas also had a home in Oakland and that he used a GMC Blazer truck to transport chemicals and glassware to the laboratory. Given Freitas’ background — his May 1980 arrest for importing seven pounds of cocaine and his January 1982 arrest for attempting to involve his brother-in-law in a methamphetamine-making scheme — the informant’s tips added to the picture of Freitas as someone who was not unfamiliar with drugs. In October 1984, sheriffs around Clearlake notified the DEA that hoses ran from Freitas’ house to the lake and that neighbors had noticed strong odors around the house. Both the odors and the hoses are signs of a methamphetamine laboratory. The anonymous informant phoned DEA agents twice in November, telling them that Freitas would probably begin producing methamphetamine soon, and phoned twice in December, telling them *1453 that the drug-making operation would occur either at Freitas’ home in Clearlake or at a location north of Sacramento.

On December 9, 1984, the informant called again and told the agency that Frei-tas was loading equipment for the manufacture of methamphetamine; this information jibed with the observations that DEA agents made the same day when they followed Freitas. On Freitas’ trip to his home that day, one of the people in his entourage stopped at a grocery store and bought large blocks of ice, which are also used in the manufacture of methamphetamine. Two days later, someone in Freitas’ party bought even more ice. Agents observed that the windows on the ground floor of the house were covered and that a hose ran from the house to the lake.

On the basis of this information, DEA special agent Stephen Wood applied to a magistrate for eight search warrants on December 12, 1984. One warrant permitted agents to search Freitas’ Clearlake home, one warrant permitted them to search his Oakland home, and six warrants permitted them to search some storage lockers. The warrants were to be executed by December 16, 1984. On December 13, 1984, special agent Laura Hayes applied for a new search warrant — the so-called “surreptitious entry” warrant — for the Clearlake house. Hayes evidently believed that the defendants were in the middle of what would be an ongoing drug operation and that a surreptitious entry would help the DEA “determine the status of the suspected clandestine methamphetamine laboratory.” 1 Excerpt of Record (E.R.) at 115. Under the terms of this warrant, the agents were permitted to enter the home while no one else was there, look around, and leave without removing anything. The magistrate, in issuing the warrant, used a conventional warrant form, designed to comply with Rule 41, Fed.R.Crim.P., but crossed off two items: first, the description of property to be seized, and second, the requirement that copies of the warrant and an inventory of the property taken were to be left at the residence. The warrant contained no notice requirement. Agents executed the warrant on December 13,1984, at approximately 11:00 p.m.

On December 17, a day after the eight initial search warrants had expired, the government applied for an extension (until December 26, 1984) of all eight warrants. The magistrate issued the extension, and, on December 20, agents seized various evidence and arrested the defendants at the Clearlake house. The defendants were charged with two violations of 21 U.S.C. § 841 (a)(1) (1982) (possession of a controlled substance with intent to manufacture and distribute) and with one violation of 21 U.S.C. § 846 (1982) (conspiracy to violate § 841(a)(1)).

On May 6, 1985, the district court, pursuant to a motion to suppress, conducted a limited hearing on, first, the training and information given to DEA agents regarding the requirements for obtaining search warrants, second, the availability of alternatives to surreptitious entry in investigating a possible laboratory operation, and third, the danger of the chemicals used to make methamphetamine. Because the government questioned whether codefend-ants Walter Freitas and Jonny McClellan had standing, 1 the district court discussed the legality of only Raymond Freitas’ search. Applying the “totality of the circumstances” test, the court found that the informant’s tips had been reliable and that the magistrate had justifiably found probable cause to issue the December 12 warrant. The court also noted that, standing alone, the magistrate’s “extension,” on December 17, of the already expired December 12 warrants was not so improper as to render the warrants invalid. But, the court added, the real issue was not whether the extension itself was improper but instead whether the surreptitious entry (and the information gleaned from that entry) im- *1454 permissibly tainted the December 17 warrant. 2 The court found that surreptitious entry warrants are neither valid under Rule 41 of the Fed.R.Crim.P. nor constitutionally permissible. In reaching the second of these conclusions, the court pointed out that, although Title III of the Omnibus Crime Control and Safe Streets Act of 1968, 18 U.S.C. §§ 2510-2520 (1982) (the wiretap requirements), was not directly applicable, “its provisions give content to the minimum standards of the Fourth Amendment as applied to electronic surveillance, and by ... analogy, a surreptitious entry.” 2 E.R. at 233. The Court held that United States v. Leon, 468 U.S. 897 , 104 S.Ct. 3405 , 82 L.Ed.2d 677 (1984), and Massachusetts v. Sheppard, 468 U.S. 981 , 104 S.Ct. 3424 , 82 L.Ed.2d 737 (1984), did not bar suppression. In denying the government’s motion for reconsideration, the court reemphasized the lack of any notice provision in the surreptitious entry warrant and held that the lack of notice violated both Rule 41 and the Fourth Amendment.

The court found that the agents’ reliance on the surreptitious entry warrant was objectively unreasonable within the meaning of Leon and Sheppard, supra, even assuming

3 E.R. at 436. The court also applied the “independent source” rule and again rejected the government’s assertion that the December 20 seizure of evidence was not tainted by the information obtained during the surreptitious entry. Finally, the court ordered a limited hearing to determine whether, under Nix v. Williams, 467 U.S. 431 , 104 S.Ct. 2501 , 81 L.Ed.2d 377 (1984), the evidence from the December 20 search and arrest was admissible under the “inevitable discovery” rule. At the hearing, the court held that the evidence would not inevitably have been discovered. Accordingly, the district court suppressed the evidence. The government appeals; we have jurisdiction under 18 U.S.C. § 3731 (1982).

II.

STANDARD OF REVIEW

Questions of interpretation of the Federal Rules are reviewed de novo. See, e.g., United States v. McClintock, 748 F.2d 1278, 1287 (9th Cir.1984) (reviewing Fed. R. of Evid. de novo), cert denied, — U.S. -, 106 S.Ct. 75 , 88 L.Ed.2d 61 (1985); Harbeson v. Parke Davis, Inc., 746 F.2d 517, 520 (9th Cir.1984) (reviewing Fed. R. Civ.P. de novo). A warrant’s facial validity is also reviewed de novo. See McClintock, 748 F.2d at 1282 . The question of whether the agents’ reliance on the warrant was objectively reasonable is a mixed question of fact and law to be given de novo review. United States v. Hendricks, 743 F.2d 653, 656 (9th Cir.1984) (citing United States v. McConney, 728 F.2d 1195, 1201 (9th Cir.) (en banc), cert. denied, 469 U.S. 824 , 105 S.Ct. 101 , 83 L.Ed.2d 46 (1984)), cert. denied, 470 U.S. 1006 , 105 S. Ct. 1362 , 84 L.Ed.2d 382 (1985). Although normally the district court’s determination of the questions of fact surrounding the warrants would be reviewed using the “clearly erroneous” standard, see McConney, 728 F.2d at 1200 , here the district court assumed, for the sake of argument, that the government’s facts were true. Therefore, it did not engage in the *1455 factfinding that is reviewed under the “clearly erroneous” standard. 3

III.

DOES RULE 41, FED.R.CRIM.P., AUTHORIZE A WARRANT PERMITTING SURREPTITIOUS ENTRY?

The district court held that a search warrant permitting agents to observe, but not “seize,” tangible property was impermissible under Rule 41. That holding conflicts with language in United States v. New York Telephone Co., 434 U.S. 159, 169 , 98 S.Ct. 364, 370 , 54 L.Ed.2d 376 (1977):

Id. (quoting Fed.R.Crim.P. 41(h)). That case held “seizures” of intangibles were not precluded by the definition of “property” appearing in Rule 41(b). 434 U.S. at 170 , 98 S.Ct. at 371 (“Rule 41 is sufficiently broad to include seizures of intangible items such as dial impulses recorded by pen registers____”); cf. United States v. Kahn, 415 U.S. 143, 154-55 , 94 S.Ct. 977, 983-84 , 39 L.Ed.2d 225 (1974) (reasonable seizure of conversations does not violate the Fourth Amendment).

Without doubt there was a “search” in this case. Its purpose, we hold, was “to seize” intangible, not tangible, property. The intangible property to be “seized” was information regarding the “status of the suspected clandestine methamphetamine laboratory.” The search was authorized by a warrant supported by what the district court concluded was probable cause. We agree with that conclusion.

The question remains, however, whether a warrant lacking both a description of the property to be seized and a notice requirement conforms to Rule 41, Fed.R.Crim.P. Ordinarily it would not. Whether it does so under the facts of this case and the holding of United States v. New York Telephone Co. is the issue we confront. Two circumstances make this issue particularly difficult. The first is that although the warrant “excused [the agents] from leaving a copy of the inventory and return [notice] on the premises,” it required the agents to furnish the magistrate with the inventory and return. 1 E.R. at 111. The second is that, although Freitas did not receive notice contemporaneous with the search, he and other defendants did receive notice within seven days of the search. 4

The application of Rule 41 to searches for the purpose of seizing only information obviously requires substantial interpretation of its terms. The crucial question pertains to notice. In what manner should Rule 41(d) be applied to warrants authorizing clandestine entries? A return to the magistrate, as required by the warrant here, obviously provides a “return” that can be deemed to satisfy the return requirement of Rule 41(d). Similarly, reasonably prompt notice to the person whose premises were searched for information only might be deemed to supply the Rule’s notice requirement. Because the adjustments to Rule 41 necessary to regulate surreptitious entries can better be accomplished by the rulemakers and Congress than by the case-by-case work of courts, we are reluctant to hold that the warrant in *1456 this case conformed to Rule 41(d). Therefore, we hold that there was no compliance with Rule 41 under the facts of this case.

The failure to comply with Rule 41 does not automatically require suppression of the property seized by way of the search. Assuming the search and seizure does not transgress the Fourth Amendment’s commands, this court has held that suppression is required only where agents would not have carried out the search and seizure had they been required to follow the rule and where they “intentional[ly] and deliberately] disregardfed] ... a provision in the Rule.” United States v. Stefanson, 648 F.2d 1231, 1235 (9th Cir.1981) (quoting United States v. Radlick, 581 F.2d 225, 228 (9th Cir.1978)). Application of this standard, however, may be unnecessary if the search and seizure was barred by the Fourth Amendment. We turn to that question.

IV.

APPLICATION OF THE FOURTH AMENDMENT TO THE SEARCH

The surreptitious character of the search and seizure in this case calls to mind wiretapping, which is now governed by Title III of the Omnibus Crime Control and Safe Streets Act of 1968, 18 U.S.C. §§ 2510-2520 (1982). The district court held that noncompliance both with Title Ill’s notice provisions and with the “necessity for electronic surveillance requirement” existed in this case. Reasoning by analogy, the district court held the search and seizure violated the Fourth Amendment.

Despite the similarity of the problems presented by this case and wiretapping, Title III has been held to apply only to aural interception of communication, see New York Telephone Co., 434 U.S. at 166-67 , 98 S.Ct. at 369-70 , and not to visual observations. Title III, however, does serve to make clear the probable constitutional importance of both the necessity for the surreptitious seizure and the subsequent notice.

With respect to a necessity requirement, the record before us fails to show that it was met. Perhaps it could have been but, viewing the record as a whole, we conclude that it merely demonstrates that the search and seizure would facilitate the investigation of Freitas, not that it was necessary. We hasten to add, however, that we do not hold that a showing of necessity is constitutionally required in a case such as is before us. We merely wish to point out that any such showing is lacking here and that, had such a showing been made, it could have strengthened the claim that the search and seizure in this case met the commands of the Fourth Amendment.

The absence of a notice requirement in the warrant presents a much more difficult issue. While it is clear that the Fourth Amendment does not prohibit all surreptitious entries, see Dalia v. United States, 441 U.S. 238, 247 , 99 S.Ct. 1682, 1688 , 60 L.Ed.2d 177 (1979), it is also clear that the absence of any notice requirement in the warrant casts strong doubt on its constitutional adequacy, see Berger v. New York, 388 U.S. 41, 60 , 87 S.Ct. 1873, 1884 , 18 L.Ed.2d 1040 (1967). We resolve those doubts by holding that in this case the warrant was constitutionally defective in failing to provide explicitly for notice within a reasonable, but short, time subsequent to the surreptitious entry. Such time should not exceed seven days except upon a strong showing of necessity.

We take this position because surreptitious searches and seizures of intangibles strike at the very heart of the interests protected by the Fourth Amendment. The mere thought of strangers walking through and visually examining the center of our privacy interest, our home, arouses our passion for freedom as does nothing else. That passion, the true source of the Fourth Amendment, demands that surreptitious entries be closely circumscribed. The warrants in this case failed to do so.

V.

THE GOOD FAITH EXCEPTION

It follows that the suppression order of the district court was proper insofar *1457 as it rested upon the warrant’s failure to comply with Rule 41 or the Fourth Amendment. We hold, however, that the district court erred in holding that on the basis of the actual and assumed facts the agents were not entitled to assert that their reliance on the warrant was objectively reasonable and that, as a consequence, the December 17 warrant was impermissibly tainted by the surreptitious search and seizure.

United States v. Leon, 468 U.S. 897 , 104 S.Ct. 3405 , 82 L.Ed.2d 677 (1984), lists four circumstances in which an agent could not claim that his reliance on a warrant was objectively reasonable. The two relevant circumstances here are, first, if the affidavit upon which the warrant was issued was “ ‘so lacking in indicia of probable cause as to render official belief in its existence entirely unreasonable,’ ” id. at 923 , 104 S.Ct. at 3422 (quoting Brown v. Illinois, 422 U.S. 590, 611 , 95 S.Ct. 2254, 2265 , 45 L.Ed.2d 416 (1975) (Powell, J., concurring in part)), and second, if the warrant either “fail[ed] to particularize the place to be searched or the things to be seized,” id. at 923, 104 S.Ct. at 3422. Neither of those circumstances is present in this case. The warrant described the place to be searched (Freitas’ Clearlake residence) and the items to be observed (evidence of a drug laboratory), and the affidavit upon which the request for the warrant was based referred to that of the previous day (Dec. 12).

In the companion case to Leon, Massachusetts v. Sheppard, 468 U.S. 981 , 104 S.Ct. 3424 , 82 L.Ed.2d 737 (1984), the Court described the type of behavior that would render an agent’s reliance on an invalid warrant objectively reasonable. The detective in Sheppard showed his affidavit to the district attorney, and the district attorney approved it; the detective then gave the approved affidavit to a judge, who found that probable cause existed; the detective asked the judge to change the warrant form because the agent had not been able to find a copy of the correct form for the particular search requested, and the judge made some changes. Id. at 985-86 , 104 S.Ct. at 3427. In fact, the Court went on to explain that, if “[a]n error of constitutional dimensions may have been committed with respect to the issuance of the warrant,” the fault was the judge’s and did not affect the determination of the officer’s objective reasonableness. Id. at 990, 104 S.Ct. at 3429. Although the district court in this case assumed that the agents had heard of similiar surreptitious entry warrants issued elsewhere, that the agents had asked the advice of an Assistant U.S. Attorney, and that the agents discussed the surreptitious entry with the magistrate, it concluded that the agents’ reliance on the warrant was objectively unreasonable. In light of Sheppard , this conclusion is incorrect. Furthermore, on the basis of those assumptions, “[tjhis is not an instance in which ‘it is plainly evident that a magistrate or judge had no business issuing a warrant,’ ” id. at 990 n. 7, 104 S.Ct. at 3429 n. 7 (quoting Illinois v. Gates, 462 U.S. 213, 264 , 103 S.Ct. 2317, 2346 , 76 L.Ed.2d 527 (1983) (White, J., concurring)). It follows if the facts support these assumptions, that the agents were objectively reasonable, that the December 17 warrant was valid, and that the suppression order was improper.

YI.

THE REMAND

Because the district court did not find, but merely assumed, certain crucial facts we deem essential to invoking the good faith exception, we must remand this case to the district court to permit it to make explicit findings with respect to these facts. The remand is limited, however. Should the district court make findings consistent with its four assumptions set forth at 3 E.R. 436-37, it should withdraw its order suppressing evidence of drug-related activity. Should the district court find one or more of these assumptions not supported by the facts, the good faith exception on the basis of Leon and Sheppard must be applied by the district court to the facts as they are found to be. The possibility of *1458 suppression for violation of Rule 41 remains. We leave it to the district court to address that question independently. . Its resolution, of course, should consider our analysis of Rule 41 as well as our holding that, under the facts it assumed, the agents’ conduct did not violate the good-faith standard the Supreme Court erected in Leon and Sheppard .

REVERSED AND REMANDED FOR PROCEEDINGS CONSISTENT WITH THIS OPINION.

. The government withdrew its objection to Jon-ny McClellan’s and Walter Freitas’ standing in the motion to suppress, and the district court granted the two defendants’ joinder in the motion to suppress on July 10, 1985.

. The district court, citing United States v. Fo-garty, 663 F.2d 928, 930 (9th Cir.1981) (per cu-riam), found that agent Hayes' affidavit was supported by the previous day’s affidavit (agent Wood’s affidavit) and that therefore the magistrate had enough information before him to find probable cause to issue the surreptitious entry warrant.

. If the district court had engaged in actual factfinding, this court could overturn the district court’s findings only if ‘“the reviewing court on the entire evidence is left with the definite and firm conviction that a mistake has been committed.’ ” Anderson v. City of Bessemer City, 470 U.S. 564 , 105 S.Ct. 1504, 1511 , 84 L.Ed.2d 518 (1985) (quoting United States v. United States Gypsum Co., 333 U.S. 364, 395 , 68 S.Ct. 525, 542 , 92 L.Ed. 746 (1948)).

. United States v. New York Telephone Co., 434 U.S. 159 , 98 S.Ct. 364 , 54 L.Ed.2d 376 (1977), noted that Rule 41 does not require notice to be given prior to the search. Id. at 169 n. 16, 98 S.Ct. at 371 n. 16. In this case, however, we are not concerned with the concepts of prior or contemporaneous notice; rather, our concern focuses on the issue of post-search notice.