It depends.  Normally, under Virginia law, the police must: (1) knock; (2) identify themselves as police officers; (3) indicate the reason for their presence; and (4) wait a reasonable time for the occupants to answer the door.  As with everything else in the law, there are exceptions to this requirement.  The police may enter without the required notice if announcing their presence would be dangerous for them, or would allow the occupants to escape, or would result in the destruction of evidence.  The police just have to have a reasonable suspicion that one of these factors is present before executing a no-knock warrant.  As opposed to some states, Virginia requires the police to satisfy this test in each case rather than exempt a whole class of cases, such as drug cases where the evidence can be destroyed.  Each case is different and the magistrate cannot order a no-knock warrant.  This rule also does not apply if the occupant gives consent for the police to enter, even if the consent was obtained by a ruse or false statements.  If you have questions about search warrants, please contact Gene Cox at Coxfedlaw, LLC for a free consultation.