Document ID: ./input/supremecourt_opinions/opinions/17pdf/16-402_h315.pdf
Page Number: 25

Cite as:  585 U. S. ____ (2018) 

21 

Opinion of the Court 

subpoena  for  no  reason  other  than  “official  curiosity.” 
United  States  v.  Morton  Salt  Co.,  338  U. S.  632,  652 
(1950).  JUSTICE  KENNEDY  declines  to  adopt  the  radical 
implications  of  this  theory,  leaving  open  the  question 
whether the warrant requirement applies “when the Gov-
ernment  obtains  the  modern-day  equivalents  of  an  indi-
vidual’s  own  ‘papers’  or  ‘effects,’  even  when  those  papers
or  effects  are  held  by  a  third  party. ”  Post,  at  13  (citing 
United  States  v.  Warshak,  631  F. 3d  266,  283–288  (CA6 
2010)).  That  would  be  a  sensible  exception,  because  it 
would prevent the subpoena doctrine from overcoming any
reasonable  expectation  of  privacy.    If  the  third-party  doc-
trine does not apply to the “modern-day equivalents of an
individual’s own ‘papers’ or ‘effects,’ ” then the clear impli-
cation  is  that  the  documents  should  receive  full  Fourth 
Amendment  protection.  We  simply  think  that  such  pro-
tection should extend as well to a detailed log of a person’s
movements over several years.

This is certainly not to say that all orders compelling the
production  of  documents  will  require  a  showing  of  proba-
ble cause.  The Government will be able to use subpoenas
to  acquire  records  in  the  overwhelming  majority  of  inves-
tigations.  We hold only that a warrant is required in the
rare  case  where  the  suspect  has  a  legitimate  privacy  in-
terest in records held by a third party.

Further,  even  though  the  Government  will  generally 
need  a  warrant  to  access  CSLI,  case-specific  exceptions
may  support  a  warrantless  search  of  an  individual’s  cell-
site  records  under  certain  circumstances.    “One  well-
recognized  exception  applies  when  ‘ “the  exigencies  of  the 
situation”  make  the  needs  of  law  enforcement  so  compel-
ling  that  [a]  warrantless  search  is  objectively  reasonable 
under  the  Fourth  Amendment.’ ”    Kentucky  v.  King,  563 
U. S. 452, 460 (2011) (quoting Mincey v. Arizona, 437 U. S. 
385,  394  (1978)).  Such  exigencies  include  the  need  to 
pursue  a  fleeing  suspect,  protect  individuals  who  are