"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."
-the Fourth Amendment
Security is vital to the well being of the individual the community and the state. The three are not always mutually exclusive, but they tend to come into conflict a lot more than you'd think. Security for one can mean that the other two may not have security and it seems like all three are in a tug of war, but the Founders felt that it was the Individual, that was the important one to protect. Why? Well who are States made up of? The first step to and State becoming oppressive and ultimately destructive is to discount the security of the individual.
Again its important to note that this doesn't protect you from nature, or from other citizens this is protection from the government. So in practical terms this means that before the Police can search your house for anything incriminating, or to come and arrest you they need a warrant. Here's the catch, "Probable cause". See if I were to call a Police officer, say my house is being robbed, the Police come, and I am clearly high, and there's no evidence of any wrong doing at all, then there's reasonable assumption that there might in fact be drugs in the house. They can't toss the place, but if I am a dumb ass and leave my crack needles out in the open, well, they've got me.
But If I, a law abiding citizen had something illegal in my possession, then the Police can not come and search me or take any of my things. If I am sitting on a park bench minding my own business a cop can't come and take me to jail, unless I have committed a crime in front of him, say sitting naked on a bench in the park. Also in practical terms, The warrant has to state exactly where they will search and what methodology they will use to uncover any evidence. Say there's a Search and Seizure warrant and the police are looking for the President's missing Cohones. Well they can open drawers and look (carefully) for them, but if they're say hidden in an air vent, unless the warrant specifically states so, or someone tells them that its there, they can not go scrounging through my vents.
The real tricky bit about this Amendment is the Exclusionary Rule, which in essence states that evidence can be dropped or "forgotten" about a case if it was obtained "illegally". Its different from state to state, and even in each court room what is and is not admissible, but more times then we'd care to think about vital evidence was left out of a case because some T wasn't crossed or I wasn't dotted. It is maddening and frustrating, but believe it or not it is far far better than the alternative.
Another practicality that has actually given us a headache is the Patriot Act and the TSA. I personally think that the TSA would be well within their right (and damned well should!) profile when doing a screening. I doubt highly that Granny whose 80 years old is going to hijack a plane. So where is the line? The problem is that Air Travel is a Service, and the TSA, incompetent as it is, is necessary to prevent tragic consequences. I believe though that should any idiot try to take over the plane you'll see what I have dubbed the Flight 93 effect. In essence, the Passengers WILL fight back. I can see screening your bags for explosives, and you can do that without being intrusive. I can even see taking a person who is behaving belligerently for further screening, but at the core I believe the current methodology violates the 4th Amendment.
The Patriot Act seemed like a good idea at the time, and if you are just sitting back looking for trends, then it is fine as a tool. If Mohamed is calling Saudi, Pakistan, and Yemen every other day, then that might be a good idea to take a look at him. But to actually tap his phone you do need a warrant. Further than that any arrests better damn well have a good reason. I am actually ok with not giving someone a lawyer right away, if they are in the act of committing a terrorist act, which is at its core an act of war, and not a normal crime. But you'd better damn well catch him or her in the act. Here, sting operations where a dumb ass builds a fake bomb with an FBI agent watching them the whole time. . . well actually I'd rather that than the dumb ass actually blows something up. In this particular case you are not violating the 4th Amendment because this action was of the subject's own free will.
My take is that there are fine, but distinct lines here. We need to understand that there will be times that the individual will need to act in such a manner that he may not be as "free" as they would like, but that line is also distinct. the second you cross it, the state has become destructive to its own citizen's well being.