Document ID: ./input/supremecourt_opinions/opinions/17pdf/16-402_h315.pdf
Page Number: 22.0

18 

CARPENTER v. UNITED STATES 

Opinion of the Court 

interval).  We do not disturb the application of Smith and 
Miller  or  call  into  question  conventional  surveillance
techniques and tools, such as security cameras.  Nor do we
address  other  business  records  that  might  incidentally
reveal location information.  Further, our opinion does not
consider  other  collection  techniques  involving  foreign 
affairs or national security.  As Justice Frankfurter noted 
when considering new innovations in airplanes and radios,
the  Court  must  tread  carefully  in  such  cases,  to  ensure 
that  we  do  not  “embarrass  the  future.”    Northwest  Air-
lines, Inc. v. Minnesota, 322 U. S. 292, 300 (1944).4 

IV 
Having  found  that  the  acquisition  of  Carpenter’s  CSLI
was a search, we also conclude that the Government must 
generally  obtain  a  warrant  supported  by  probable  cause 
before  acquiring  such  records.  Although  the  “ultimate 
measure of the constitutionality of a governmental search
is  ‘reasonableness,’ ”  our  cases  establish  that  warrantless 
searches  are  typically  unreasonable  where  “a  search  is 
undertaken  by  law  enforcement  officials  to  discover  evi-
dence of criminal wrongdoing.”  Vernonia School Dist. 47J 
v.  Acton,  515  U. S.  646,  652–653  (1995).    Thus,  “[i]n  the
absence of a warrant, a search is reasonable only if it falls 
within  a  specific  exception  to  the  warrant  requirement.” 
Riley, 573 U. S., at ___ (slip op., at 5).

The Government acquired the cell-site records pursuant
to a court order issued under the Stored Communications 
Act,  which  required  the  Government  to  show  “reasonable 
grounds” for believing that the records were “relevant and 

—————— 

4 JUSTICE  GORSUCH  faults  us  for  not  promulgating  a  complete  code 
addressing the manifold situations that  may be presented by this new 
technology—under  a  constitutional  provision  turning  on  what  is  “rea-
sonable,”  no  less.  Post,  at  10–12.    Like  JUSTICE  GORSUCH,  we  “do  not 
begin to claim all the answers today,” post, at 13, and therefore decide 
no more than the case before us.