At airports you have no right to privacy, because you are choosing to fly, and therefore are subject to their rules.
I know, and I think it's bullshit. The problem is that it's no difference than a British officer having a writ of assistance, which was the entire reason for the 4th amendment being guaranteed anyhow. If a LEO has full discretion on who he/she searches then it opens the door for racial profiling. How big of a deal is it to just detain them until you can get a warrant. It will take longer (they may miss their flight), but I am sure a process could be put in place to speed it up.
The only time you can be searched, is if an officer catches you in the act of a crime. (or I believe something about suspicious activity, idk).
For a misdemeanor, they must actually witness the crime in order to arrest you. However for a felony, they only need suspicion that you committed the crime. Once a lawful arrest has taken place they can search you without a warrant.
A warrant must be obtained to search someone that is just suspected to be involved in something.
There are a lot of exceptions. 4th amendment only applies in places where you have a reasonable expectation of privacy. Since your car is not one of these places. An officer can search areas in a car where a weapon could be concealed. With suspicion, he can search anywhere, even without a warrant.
A few other exception I have read about:
On a public school ground you can be searched without a warrant if the officer has reasonable grounds to believe that the search will result in finding evidence for illegal activity.
Government employees in a government building can be searched without a warrant for the same reasons above.
Finally, a search is reasonable if the target without coercion consents to the search, even if the target is unaware and not told about their right to refuse to cooperate.
The last one is really bullshit. An officer should be required to inform you of your right to refuse.