When Have I Been "Seized?"
Did you know that a person can be seized? Of course you knew that - you've undoubtedly heard of "arrest." But what about that seizure that is somewhere between arrest and "no where to run." All of this matters because if you have been "seized" there is a duty to advise you of your right to remain silent if the police are interrogating you. Consider this scenario - cops come to your door and say they smell marijuana. They have a tip that you possess and maybe sell mary jane. "Can we come in," they ask.
"No way, Dude," you respond.
"Why not? You got something to hide?"
"Nothing I want to share with you."
So do they leave? Not a chance. Instead they give you the "knock and talk" line: "Look, we smell marijuana. We can make you sit here while we get a warrant and that could take hours, or you could sign the consent. Unless we find the Lindberg baby, we won't arrest anyone today if you let us search. If not - well Dude, you get the picture, right? So sign right here."
If you sign and consent to the search, you may still have a claim that will invalidate the search. The short answer here is that the officers "seized" you when they showed up at your door and would not let you leave ("we can get a warrant"). If you don't think you can scoot (officers, and uniforms and guns and such) then you likely have had your liberty restricted. That may lead to the suppression of any evidence the police found inside the apartment and any incriminating statements you made - like "hey that's medical marijuana, I'm from Oregon."
If the cops have knocked at your door and you have talked your way into criminal charges, call a lawyer and check out the law on your particular situation. If you have this situation occur, I suggest that you tell them to get a warrant. The mere smell of marijuana is not probable cause to arrest without more, and likely there won't be more. Protect your rights to be free from an unreasonable search with these power words:
"Get a warrant, if you can, please."
And be polite.
Sure, this is good advice, but you don't mention what happens if you close the door in their face.
They will say they "heard noises" which through their training and experience means that you are destroying evidence - creating exigent circumstances allowing them to kick down your door.