Trash. The things you leave outside your home at the edge of your property are unprotected by the Fourth Amendment. For example, once you carry your trash out of your house or office and put it on the curb or in the dumpster for collection, you have given up any expectation of privacy in the contents of that trash. You should always keep this in mind when you are disposing of sensitive documents or anything else that you want to keep private. You may want to shred all paper documents and destroy all electronic media. You could also try to put the trash out (or unlock your trashcan) right before it’s picked up, rather than leaving it out overnight without a lock.
Public places. It may sound obvious, but you have little to no privacy when you are in public. When you are in a public place — whether walking down the sidewalk, shopping in a store, sitting in a restaurant or in the park — your actions, movements, and conversations are knowingly exposed to the public. That means the police can follow you around in public and observe your activities, see what you are carrying or to whom you are talking, sit next to you or behind you and listen to your conversations — all without a warrant. You cannot necessarily expect Fourth Amendment protection when you’re in a public place, even if you think you are alone. Fourth Amendment challenges have been unsuccessfully brought against police officers using monitoring beepers to track a suspect’s location in a public place, but it is unclear how those cases might apply to more pervasive remote monitoring, like using GPS or other cell phone location information to track a suspect’s physical location.
Infiltrators and undercover agents. Public meetings of community and political organizations, just like any other public places, are not private. If the government considers you a potential criminal or terrorist threat, or even if they just have an unfounded suspicion that your organization might be up to something, undercover police or police informants could come to your public meetings and attempt to infiltrate your organization. They may even wear hidden microphones and record every word that’s said. Investigators can lie about their identities and never admit that they’re cops — even if asked directly. By infiltrating your organization, the police can identify any of your supporters, learn about your plans and tactics, and could even get involved in the politics of the group and influence organizational decisions. You may want to save the open-to-the-public meetings for public education and other non-sensitive matters and only discuss sensitive matters in meetings limited to the most trusted, long-time staff and constituents.
Importantly, the threat of infiltrators exists in the virtual world as well as the physical world: for example, a police officer may pose as a online "friend" in order to access your private social network profile.
Records stored by others. As the Supreme Court has stated, "The Fourth Amendment does not prohibit the obtaining of information revealed to a third party and conveyed by him to Government authorities, even if the information is revealed on the assumption that it will be used only for a limited purpose and the confidence placed in the third party will not be betrayed." This means that you will often have no Fourth Amendment protection in the records that others keep about you, because most information that a third party will have about you was either given freely to them by you, thus knowingly exposed, or was collected from other, public sources. It doesn’t necessarily matter if you thought you were handing over the information in confidence, or if you thought the information was only going to be used for a particular purpose.
Therefore it is important to pay close attention to the kinds of information about you and your organization’s activities that you reveal to third parties, and work to reduce the amount of private information you leave behind when you go about your daily business.
Opaque containers and packages. Even when you are in public, you have a reasonable expectation of privacy in the contents of any opaque (not see-through) clothes or containers. So, unless the police have a warrant or qualify for one of the warrantless search exceptions discussed below, they can’t go digging in your pockets or rummaging through your bags.
Laptops, pagers, cell phones and other electronic devices are also protected. Courts have generally treated electronic devices that hold data as if they were opaque containers.
However, always keep in mind that whatever you expose to the public isn’t protected. So, if you’re in a coffee shop using your laptop and an FBI agent sitting at the next table sees what you are writing in an email, or if you open your backpack and the FBI agent can see what’s inside, the Fourth Amendment won’t protect you.
Postal mail. The mail that you send through the U.S. Postal Service is protected by the Fourth Amendment, and police have to get a warrant to open it in most cases.
If you’re using the U.S. Postal Service, send your package using First Class mail or above. Postal inspectors don’t need a search warrant to open discount (media) rate mail because it isn’t supposed to be used for personal correspondence.
Keep in mind that although you have privacy in the contents of your mail and packages, you don’t have any privacy in the "to" and "from" addresses printed on them. That means the police can ask the post office to report the name and address of every person you send mail to or receive mail from — this is called a "mail cover" — without getting a warrant. Mail covers are a low-tech form of "traffic analysis," which we’ll discuss in the section dealing with electronic surveillance.
You don’t have any privacy in what you write on a postcard, either. By not putting your correspondence in an envelope, you’ve knowingly exposed it, and the government can read it without a warrant.
The police may be able to come into your home or office if you have opened those places to the public — but you can also ask them to leave, just as if they were any other members of the public. If they don’t have a warrant, or don’t qualify for any of the warrant exceptions, they have no more right to stay once you’ve asked them to leave than any other trespasser. However, undercover agents or officers need not announce their true identities, so asking all cops to leave the room before a meeting is not going provide any protection.
Search Warrants Are Generally Required For Most Searches and Seizures.
The Fourth Amendment requires that any search or seizure be reasonable. The general rule is that warrantless searches or seizures are automatically unreasonable, though there are many exceptions.
To get a warrant, investigators must go to a neutral and detached magistrate and swear to facts demonstrating that they have probable cause to conduct the search or seizure. There is probable cause to search when a truthful affidavit establishes that evidence of a crime will probably be found in the particular place to be searched. Police suspicions or hunches aren't enough — probable cause must be based on actual facts that would lead a reasonable person to believe that the police will find evidence of a crime.
In addition to satisfying the Fourth Amendment's probable cause requirement, search warrants must satisfy the particularity requirement. This means that in order to get a search warrant, the police have to give the judge details about where they are going to search and what kind of evidence they are searching for. If the judge issues the search warrant, it will only authorize the police to search those particular places for those particular things.