MEMORANDUM *

Appellant Michael Fritts appeals his judgment of conviction after entering a guilty plea to bank robbery, in violation of 18 U.S.C. § 2113 (a). Fritts argues that the district court erred in (1) denying his motion to suppress his statements on the grounds of pre-arraignment delay under 18 U.S.C. § 3501 (c); (2) denying his motion to suppress his statements on the grounds of involuntariness; (3) finding that he voluntarily consented to a search of his apartment; (4) finding that the FBI agents did not violate the knock-notice rule of 18 U.S.C. § 3109 in executing the federal arrest warrant; and (5) applying a two-level specific offense characteristic upward adjustment under U.S.S.G. § 2B3.1(b)(2)(F) for a “threat of death” during the commission of a robbery. We have jurisdiction pursuant to 28 U.S.C. § 1291 , and we affirm.

1. The district court properly denied Fritts’s motion to suppress his statements on the grounds of pre-arraignment delay. Rule 5(a) of the Federal Rules of Criminal Procedure requires that an arrested defendant be brought before a judicial officer “without unnecessary delay.” 18 U.S.C. § 3501 (c), in turn, creates a six hour “safe harbor” for confessions elicited before an arraignment. A court may “admit a statement made outside of the safe harbor if the delay was reasonable or if public policy concerns weigh in favor of admission.” United States v. Padilla Mendoza, 157 F.3d 730, 731 (9th Cir.1998), United States v. Van Poyck, 77 F.3d 285, 289 (9th Cir.1996).

The district court concluded that the thirty-two hour pre-arraignment delay in this ease was reasonable because Fritts was suffering from heroin withdrawal and had to be hospitalized. Relying on our decision in United States v. George, 987 F.2d 1428 (9th Cir.1993), it held that “a delay caused by medical necessity does not violate Rule 5(a).” See George, 987 F.2d at 1431 (holding that a confession made before arraignment was admissible because medical necessity was the reason for the pre-arraignment delay). The district court did not clearly err in finding that (i) “an AUSA attempted to have Defendant arraigned before Judge Battaglia as soon as possible but that Judge Battaglia refused to arraign Defendant at the hospital as a matter of court policy;” (ii) there was no evidence that the agents purposefully delayed bringing the defendant to be arraigned so they could question him; and (iii) the agents brought the defendant to the courthouse to be arraigned the same day defendant was released.

*767 2. Nor did the district court err in denying Fritts’s motion to suppress his hospital statements on the grounds of involuntariness. Considering the “totality of the surrounding circumstances,” Schneckloth v. Bustamante, 412 U.S. 218 , 93 S.Ct. 2041 , 36 L.Ed.2d 854 (1973), the court did not err in finding Fritts’s hospital statements to have been made voluntarily. “Coercive police activity is ‘a necessary predicate’ to finding a confession involuntary.” United States v. Kelley, 953 F.2d 562, 565 (9th Cir.1992) (quoting Colorado v. Connelly, 479 U.S. 157, 167 , 107 S.Ct. 515 , 93 L.Ed.2d 473 (1986)). Here, the district court found that “none of the evidence suggests that agents employed any kind of physical or psychological force to induce defendant into making statements.” Fritts waived his Miranda rights in writing, choosing to speak with the agents. Fritts was given food, treatment, medicine, and access to doctors. Although defendant contended that he believed if he did not cooperate with the agents he would be detained indefinitely at the hospital, there was no evidence to support that belief.

3. The district court did not err in finding that Fritts voluntarily consented to a search of his apartment. A person may waive his Fourth Amendment rights by consenting to a warrantless search. Schneckloth, 412 U.S. at 222 , 93 S.Ct. 2041 . “Although the Constitution does not require ‘proof of knowledge of a right to refuse as the sine qua non of an effective consent to a search,’ such knowledge [is] highly relevant to the determination that there ha[s] been consent.” United States v. Mendenhall, 446 U.S. 544, 558-59 , 100 S.Ct. 1870 , 64 L.Ed.2d 497 (1980) (quoting Schneckloth, 412 U.S. at 234 , 93 S.Ct. 2041 ); United States v. Childs, 944 F.2d 491, 496 (9th Cir.1991). Fritts executed a written consent form, expressly permitting the apartment search. The form clearly stated that he could refuse to sign it. Fritts testified that he read the consent form, and that the FBI agent also read the form to him. Although Fritts testified that the agents told him that if he consented to the search they “would not mess with his wife,” the district court did not clearly err when it found, “viewing the statement in context,” that it was an assurance that Fritts’s wife would not be harmed in the course of the search, and not a threat of harm if Fritts refused to consent. Given that “[k]nowledge of the right to refuse consent is highly relevant in determining whether a consent is valid,” Childs, 944 F.2d at 496 , and that our “review under the clearly erroneous standard is significantly deferential requiring a ‘definite and firm conviction that a mistake has been committed,’ ” Concrete Pipe & Prods, v. Construction Laborers Pension Trust, 508 U.S. 602, 623 , 113 S.Ct. 2264 , 124 L.Ed.2d 539 (1993) (citation omitted), the district court did not clearly err in finding that Fritts voluntarily consented to the search of his apartment.

4. The FBI agents did not violate the knock-notice rule of 18 U.S .C. § 3109 in executing the federal arrest warrant for Fritts. Section 3109 allows an officer with a warrant to “break open any outer or inner door or window of a house” only after giving “notice of his authority and purpose.” Here, Fritts opened the door, and therefore the requirements of the statute were never invoked. See United States v. Phillips, 149 F.3d 1026, 1029 (9th Cir.1998) (holding that § 3109 “does not apply to officers who enter through open doors”), cert. denied, 526 U.S. 1052 , 119 S.Ct. 1359 , 143 L.Ed.2d 520 (1999); United States v. Valenzuela, 596 F.2d 1361, 1365 (9th Cir.1979) (“entry through an open door is not a ‘breaking’ within the meaning of the statute”).

*768 5. The district court’s factual finding that Fritts made a “threat of death” during the commission of the robbery was not clearly erroneous. The government submitted the sworn affidavit of the victim, Lisa Richardson, which repeated the statement she gave the FBI shortly after the robbery. Because Richardson’s identity was disclosed and her contemporaneous statement and affidavit were presumptively reliable, United States v. Alonso, 48 F.3d 1536, 1546 (9th Cir.1995), the district court did not abuse its discretion in applying a two-level increase to Fritts’s offense level pursuant to U.S.S.G. § 2B3.1(b)(2)(F)

AFFIRMED.

This disposition is inappropriate for publication and may not be cited to or by the courts of this circuit except as may be provided by 9th Cir. R. 36-3.