There are certain scenarios in which law enforcement officials do not need to secure a warrant to execute a search or bring an individual into custody.
Some of these exceptions include:
Consensual searches
Searches incident to valid arrests
Brief investigatory searches (i.e., Terry stops)
Items seized in plain view (i.e., contraband sitting with sight of a law enforcement official)
Exigent circumstances (i.e., preserve evidence, prevent escape, etc.)
If you believe that your rights under the Fourth Amendment have been violated in any way by law enforcement officials, please consider speaking with an experienced legal professional who can determine what happened and take the necessary actions.