Document ID: ./input/supremecourt_opinions/opinions/17pdf/16-402_h315.pdf
Page Number: 6.0

2 

CARPENTER v. UNITED STATES 

Opinion of the Court 

a minute whenever their signal is on, even if the owner is 
not  using  one  of  the  phone’s  features.    Each  time  the 
phone connects to a cell site, it generates a time-stamped
record known as cell-site location information (CSLI).  The 
precision  of  this  information  depends  on  the  size  of  the
geographic  area  covered  by  the  cell  site.    The  greater  the 
concentration  of  cell  sites,  the  smaller  the  coverage  area.
As  data  usage  from  cell  phones  has  increased,  wireless
carriers have installed more cell sites to handle the traffic. 
That  has  led  to  increasingly  compact  coverage  areas, 
especially in urban areas.

Wireless  carriers  collect  and  store  CSLI  for  their  own 
business  purposes,  including  finding  weak  spots  in  their 
network  and  applying  “roaming”  charges  when  another 
carrier  routes  data  through  their  cell  sites.    In  addition, 
wireless  carriers  often  sell  aggregated  location  records  to
data brokers, without individual identifying information of 
the  sort  at  issue  here.    While  carriers  have  long  retained 
CSLI  for  the  start  and  end  of  incoming  calls,  in  recent 
years  phone  companies  have  also  collected  location  infor-
mation  from  the  transmission  of  text  messages  and  rou-
tine  data  connections.    Accordingly,  modern  cell  phones 
generate increasingly vast amounts of increasingly precise 
CSLI. 

B 
In  2011,  police  officers  arrested  four  men  suspected  of
robbing a series of Radio Shack and (ironically enough) T-
Mobile  stores  in  Detroit.    One  of  the  men  confessed  that, 
over  the  previous  four  months,  the  group  (along  with  a 
rotating cast of getaway drivers and lookouts) had robbed
nine  different  stores  in  Michigan  and  Ohio.  The  suspect
identified  15  accomplices  who  had  participated  in  the 
heists and gave the FBI some of their cell phone numbers;
the  FBI  then  reviewed  his  call  records  to  identify  addi-
tional numbers that he had called around the time of the