What are the exceptions to the Fourth Amendment warrant requirement?

[8-10] The district court properly found that defendants failed to show as a matter of law that the emergency and exigency exceptions to the Fourth Amendment warrant requirement applied. These two "exceptions are 'narrow' and their boundaries are 'rigorously guarded' to prevent any expansion that would unduly interfere with the sanctity of the home." Hopkins, 573 F.3d at 763 (quoting United States v. Stafford, 416 F.3d 1068, 1073 (9th Cir.2005)). Under the emergency excep tion, an officer may enter a home without a warrant to investigate an emergency that threatens life or limb if the officer has objectively reasonable grounds to believe that an emergency exists and that his immediate response is needed. Id. at 76364. This exception is derived from police officers' community caretaking function, allowing them to enter a home when an emergency which threatens physical harm is presented. Id. at 763. The exigency exception, in contrast, stems from police officers' investigatory function: it allows an officer to enter a residence without a warrant if he has "probable cause to believe that a crime has been or is beingcommitted and a reasonable belief that [his] entry" is needed to stop the destruction of evidence or a suspect's escape or carry out other crime-prevention or law enforcement efforts. Id. Both exceptions, however, require that the officer have an objectively reasonable belief that the circumstances justify entry. Id.