2. Plain View
3. Fenced-in (adjacent) Property
4. Open Fields
The Fourth Amendment of the U.S. Constitution states: "[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
Let's say the feds storm your home. You're arrested. Before trial, they bring out evidence that they found when searching your house. If you think the government entered your property illegally, you will likely argue before the court that your constitutional right against unreasonable searches and seizures was violated. After you make your argument, the court must consider whether the government is wholly responsible for the search and seizure.
A fundamental component of the Fourth Amendment is whether the defendant had a reasonable expection of privacy. You have to demontrate this in order to prove that your constitutional rights were violated.
Courts consider several factors, including:
In certain situations, the police can seize something in plain view (or smell, hearing, etc.) without a warrant. You're probably thinking that any evidence seized by the police would be in plain view, at least at the moment of seizure. But what about before that?
For example, police have a warrant to search a given area for specified objects, and in the course of the search they find some else incriminating. Would it be illegal if they seized it, even if they didn't have a warrant to do so? The answer is probably not. The police initially had a warrant, and they simply came across the item that was in plain view during their search.
Another example is if a cop is chasing a suspect and inadvertently comes across evidence. That would be legal. In short, if the police officer has a prior justification for an intrusion in the course of which he came inadvertently across a piece of evidence, then a seizure of that item would likely be found to be legal.
Note, however, that a police officer can't just go on an exploratory search of your property searching from one place to another until something incriminating is found. The officer doesn't have a warrant for that, and any such search and seizure violates the Fourth Amendment.
In legal terms, the property enclosing your home (like a fence or wall) is called the “curtilage”, which has always been protected by the Fourth Amendment. However, you must be careful what you think is your curtilage and your expectation of how private it's supposed to be.
According to the Supreme Court, your protection under the Fourth Amendment depends on the distance of the curtilage is to your home, whether the area is closed in, what you use it for, and what steps you've taken to keep it private from prying eyes. Most importantly, use common sense.
Paraphrasing the Supreme Court, it's common sense that we don't place private things on our front porches that would be better to put in your more secluded backyard, patio, or deck. People commonly have different expectations about what is private or not.
In American society we have come to expect various members of the public to enter upon such a driveway, e.g., Jehovah's Witnesses, the mail lady, Girl Scouts, neighbors, and friends. If any one of them observes suspiscious activity on your land, then they can be reasonably expected to report that activity to the police. That being so, the police can do the same thing.
What You Need to Know
If the police come to your private property to investigate something or for some other legitimate purpose, and they don't go any further than where a Girl Scout could go (e.g., walkways, driveways, or porches), any observation they make from that point is not covered by the Fourth Amendment.
But if they go on other parts of your property that other people wouldn't normally do without your permission, then they are violating your constitutional rights -- even if these parts are visible, for example, from outside the fence!
Keep in mind though that the police can head over to parts of your property not ordinarily used by visitors if, for example, they knock on the door and they know for sure that someone is inside the house.
Say you operate and live at a bed and breakfast (B&B) on twenty acres in the American Redoubt. One day, federal officers storm your property and inspect a stockpile of fresh cut timber that you neatly stacked on your property. They suspect that you cut the trees down from federal land without permission.
For nearly five hours, several law enforcement officials meticulously go through the stockpile of timber, moving trees from one stack to the other, making noise, etc. As it got dark, the officers put up a spotlight so they can see better. The timber stockpile was twenty feet from your B&B, but was only five feet from the B&B's parking area.
You would argue that the feds conducted an illegal search on your property. Because the pile was so close to the B&B, it would be considered within the curtilage of your home. Thus, your Fourth Amendment rights were violated. Even though the pile was close to the parking lot, which anybody could use, the official's thorough search was more than just a casual observation.
In short, you would without doubt be protected by the Fourth Amendment from a warrantless search and seizure of your property. Long story short, if you want protect some personal property from governmental instrusion, keep it close to your house but beyond the casual observations of a stranger.
Let's say we're in the middle years of the Prohibition. Our hero's name is Lester. One day, a government officer stakes out the home of Lester's dad. From a distance of 50 yards, he suddenly sees Lester hand a bottle to a shadowy person, somebody who the agent thought bootleg whiskey customer. Lester suddenly notices the agent, panics, picks up a jug from behind a tree, and high tails it into the woods.
Shortly after, the agent found a broken bottle and a broken jug in a nearby open field. Although both were broken, there was enough liquid to determine that it was whiskey. Lester gets arrested and argues that the evidence could not be brought against him because it was found in an open field. Lester loses.
As stated above, the Fourth Amendment protects people in their “persons, houses, papers and effects.” It is not extended the open fields. Thus, even though the agent technically trespassed on the Lester's dad's land, the seizure would not be found to be illegal.
Keep in mind, however, that Courts never took the word “open” and "fields" are to be taken loosely. Indeed, "open" has been applied even when the land was fenced in, posted with no tresspassing signs, and the evidence itself was not in plain view.
Similarly, “fields” is more than just green pasture or a mountain meadow. Police can intrude into thick wooded areas, vacant city lots, open beaches, reservoirs, and open waters. In short, “open fields” may include any unoccupied or undeveloped area outside of the curtilage; and an open field need be neither “open” nor a “field”.
Bottom line: Whatever you do out in a field, you can't demand privacy.
If you own a barn or a workshed that is technically outside of the curtilage, you are likely to be protected under the Fourth Amendment. If you take reasonable steps to ensure privacy, your barn is probably constitutionally protected from warrantless searches.