That's what the Supreme Court just told police in a ruling issued this week.
The Fourth Amendment is very clear in banning illegal searches and seizures. Since a decision in 1914, that rule has been accepted as "knock and announce". If the "knock and announce" didn't happen, the evidence was tossed out of court because the search was not in accordance with the Constitution. It's not like a bar was placed absurdly high here--- How difficult is it to say "Police! Open up!"?
The sad part? It was a 5-4 decision. Had this case gone to the Supremes a year ago, Sandra Day O'Connor would likely have voted to uphold the Fourth Amendment. Instead, right wing "activist judges" decided that the Fourth Amendment means nothing.
Democrats were badgered during the confirmation hearings for "Sloppy Seconds Sammy (It's gotta suck, being second choice after a woman with no judicial experience, huh?)" Alito for not filibustering him, despite the well known threat by Senate Republicans to put an end to the filibuster if they did.
Personally, I think they did the right thing. The filibuster is a useful legislative tool, and it would have been stupid to give it up to keep Sam Alito at a lower pay grade for two hours while the Senate Republicans took away the only right a minority party has. Had the Democrats been shortsighted enough to blow it that way, the "Lose Your Benefits" bill that would have completely deregulated the health insurance industry and allowed for all manner of pre-cancer screenings to be suspended would have been a surefire winner.
The filibuster is not the answer here--- The answer here is to run strong candidates and put the Republicans on the fuzzy side of the lollipop. Quit relying on the filibuster--- Win some damn races and never need it again.
When Democrats run weak, "Republican Lite" candidates, we end up losing--- You can't out-Republican a Republican, and we give up home field advantage every time we play their game.
Run a progressive, and reconnect with the voters that are staying home on election day. When your candidates are two slight variations on the same right wing ideology, we end up with a Constitution that doesn't mean much.