Police are supposed to need a warrant to search your house, but the courts have previously carved out an exception for "exigent circumstances", where (for example) the police think that a person inside may be destroying evidence (as immortalized in the 4th amendment text, which reads "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, unless the police really want in."). That gap was widened quite a bit this week when the supreme court decided that the police can use exigent circumstance to search a home, even if they're the ones that created the exigent circumstances in the first place. Police in the case claimed they "heard movement" behind the door after they had knocked and shouted "Police!", and therefore feared the occupants were destroying evidence. Apparently, the appropriate thing to do to preserve your rights when the police knock on your door is to stay perfectly still, make absolutely no noise whatsoever, and hope to God your neighbor in the next apartment doesn't flush his toilet.
And in a second blow, the Indiana Supreme Court decided that you don't have the right to resist police when they illegally enter your home, under the argument that even if it's an illegal entry, you can always sue them later rather than resist them now (lawsuits against police misconduct being so easy to win, of course).
So there you have it. The police can easily manufacturer themselves a reason to enter your house without a warrant, but even if they don't bother, there's nothing you can do to stop them anyway. What's does the 4th Amendment actually guard against anymore?