The Fourth Amendment doesn’t get a lot of press, but it’s one of the most critical pieces of our body of law.
The 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.Fourth Amendment to the US Constitution
This single amendment—triggered, as were so many of the first ten, by the British government’s failure to observe these legal niceties—forms the very basis of evidentiary law in the US.
Basically, it says this: the gummint isn’t take your stuff, or even search your property and stuff, unless it’s first gotten a duly-sworn warrant from someone in the judiciary. Said warrants must specifically describe what’s being searched, and what they intend to seize.
This is why, if a cop shows up at your house, you don’t have to let them in—unless they have a warrant. (Notably, if you do let them in, and they see something that interests them, they can use that to go get a warrant). This amendment is also why the cops can’t go getting a warrant for any little thing they like: they first need to show the judge probable cause, which means they need to show that—through means other than searching you and your stuff—they have a strong likelihood of finding what they’re after. Perhaps you’ve mouthed off in public about having a stash of illegal drugs, for example: that’s probably cause, and can be reason enough for a cop to get a warrant to come looking for the drugs.
There are a butte-tonne of exceptions. A few of the major ones:
- Consent. If you consent to the search, then a warrant isn’t needed.
- Plain view. If whatever the cop is searching for is, like, RIGHT THERE, they don’t need a a warrant.
- Your car. Generally speaking, your car isn’t considered a residence or repository of personal items, and so you have a reduced protection from warrantless searches. Also, vehicles can be moved around a lot faster than houses. Cops still need either reasonable suspicion—like you acting weird when they pull you over for a simple traffic stop—or need to be conducting a universal search checkpoint looking for, say, a kidnapper. Notably, the ability of the cops to search the car doesn’t extend to the people in it unless those people consent. Also, in most cases, if your car is parked at your house, it’s considered part of your house during that time.
The penalty on law enforcement for violating the Fourth Amendment is usually limited to the evidence thus obtained being inadmissible in court, so most of the time, cops are pretty good about following the rules. After all, if they screw up, then whatever evidence they were relying on to close their case is now off limits, which usually borks the entire case. This is called the “exclusionary rule,” and it’s actually pretty controversial.
The Fourth Amendment is also the cornerstone of the US concept of legal privacy rights, most often with regard to our privacy from government intrusion and data-gathering. This results in plenty of court cases, too, especially in our modern digital age.