Document ID: ./input/supremecourt_opinions/opinions/17pdf/16-402_h315.pdf
Page Number: 11.0

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

7 

Opinion of the Court 

what was happening within the home.  Ibid.
  Likewise  in  Riley,  the  Court  recognized  the  “immense 
storage  capacity”  of  modern  cell  phones  in  holding  that
police  officers  must  generally  obtain  a  warrant  before
searching  the  contents  of  a  phone.  573  U. S.,  at  ___  (slip 
op.,  at  17).  We  explained  that  while  the  general  rule
allowing  warrantless  searches  incident  to  arrest  “strikes 
the appropriate balance in the context of physical objects,
neither  of  its  rationales  has  much  force  with  respect  to” 
the vast store of sensitive information on a cell phone.  Id., 
at ___ (slip op., at 9). 

B 
The  case  before  us  involves  the  Government’s  acquisi-
tion  of  wireless  carrier  cell-site  records  revealing  the
location  of  Carpenter’s  cell  phone  whenever  it  made  or
received calls.  This sort of digital data—personal location 
information  maintained  by  a  third  party—does  not  fit 
neatly  under  existing  precedents.    Instead,  requests  for 
cell-site records lie at the intersection of two lines of cases, 
both  of  which  inform  our  understanding  of  the  privacy
interests at stake. 

The first set of cases addresses a person’s expectation of
privacy in his physical location and movements.  In United 
States  v.  Knotts,  460  U. S.  276  (1983),  we  considered  the 
Government’s use of a “beeper” to aid in tracking a vehicle
through  traffic.    Police  officers  in  that  case  planted  a
beeper  in  a  container  of  chloroform  before  it  was  pur-
chased  by  one  of  Knotts’s  co-conspirators.    The  officers 
(with  intermittent  aerial  assistance)  then  followed  the 
automobile  carrying  the  container  from  Minneapolis  to 
Knotts’s cabin in Wisconsin, relying on the beeper’s signal 
to help keep the vehicle in view.  The Court concluded that 
the “augment[ed]” visual surveillance did not constitute a 
search  because  “[a]  person  traveling  in  an  automobile  on 
public  thoroughfares  has  no  reasonable  expectation  of