Kyllo (defendant) was arrested for growing marijuana in his home. The police came to discover the marijuana with the use of a thermal-imaging device used to detect the heat from the high-intensity lamps used to grow the plants inside. The thermal-imaging device was used by an officer on the street outside Kyllo’s home to scan the house. The scan revealed that part of the house was significantly hotter than the rest. The police used this information to obtain a warrant to search Kyllo’s home where they found over 100 marijuana plants. Kyllo moved to suppress the evidence seized from his home, but the court denied the motion. Kyllo then entered a conditional guilty plea. The United States Court of Appeals for the Ninth Circuit affirmed the denial of the motion to suppress. The United States Supreme Court granted certiorari.