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8 

MISSOURI v. MCNEELY 

Opinion of the Court 

act without a warrant.  Id., at 771.  We further held that 
the blood test at issue was a reasonable way to recover the 
evidence  because  it  was  highly  effective,  “involve[d]  vir­
tually  no  risk,  trauma,  or  pain,”  and  was  conducted  in  a 
reasonable  fashion  “by  a  physician  in  a  hospital  environ­
ment according to accepted medical practices.”  Ibid.  And 
in conclusion, we noted that our judgment that there had 
been  no  Fourth  Amendment  violation  was  strictly  based
“on the facts of the present record.”  Id., at 772. 

Thus, our analysis in Schmerber fits comfortably within
our  case  law  applying  the  exigent  circumstances  excep­
tion.  In  finding  the  warrantless  blood  test  reasonable  in 
Schmerber, we considered all of the facts and circumstances 
of  the  particular  case  and  carefully  based  our  holding  on 
those specific facts. 

B 

The  State  properly  recognizes  that  the  reasonableness 
of  a  warrantless  search  under  the  exigency  exception  to
the warrant requirement must be evaluated based on the
totality  of  the  circumstances.  Brief  for  Petitioner  28–29. 
But  the  State  nevertheless  seeks  a  per se  rule  for  blood 
testing  in  drunk-driving  cases.    The  State  contends  that 
whenever  an  officer  has  probable  cause  to  believe  an 
individual has been driving under the influence of alcohol,
exigent  circumstances  will  necessarily  exist  because  BAC 
evidence  is  inherently  evanescent.  As  a  result,  the  State 
claims  that  so  long  as  the  officer  has  probable  cause  and 
the  blood  test  is  conducted  in  a  reasonable  manner,  it  is 
categorically reasonable for law enforcement to obtain the
blood sample without a warrant.

It  is  true  that  as  a  result  of  the  human  body’s  natural
metabolic  processes,  the  alcohol  level  in  a  person’s  blood
begins  to  dissipate  once  the  alcohol  is  fully  absorbed  and 
continues  to  decline  until  the  alcohol  is  eliminated.    See 
Skinner,  489  U. S.,  at  623;  Schmerber,  384  U. S.,  at  770–