united-states police
Why do cops in the USA not seem to use the technical &quot;blow into device&quot; test for drunk drivers?
<p>I have been watching a number of &quot;cops arrest drunk driver&quot; videos lately. In every case, they don't even mention that &quot;breathalizer&quot; or whatever they called it, but instead go into these elaborate tests that take forever, where they make the suspect walk in a line and follow their finger with their eyes and stuff like that.</p>
<p>Is there any reason that they do this now? There probably is. Was the &quot;breathalizer&quot; found to be inaccurate or something? Do they really not have a simpler and quicker way to check if somebody is drunk/impaired in the year 2021?</p>

<p>Driving &quot;under the influence&quot; doesn't always mean alcohol, field sobriety tests check for impairment, breathalyzer measures alcohol levels in the body. You can be impaired without being drunk.</p>

<p>Breathalyzers are an objective test, if they come back negative they are exculpatory evidence for the defense.  On the other hand, field sobriety tests are entirely judged by the officer at the scene, and until the prevalence of body/dash cameras, the officer's word was the only relevant testimony to whether or not the person passed or failed (and for the Horizontal Gaze Nystagmus test, i.e. the follow the pen test, it's still based pretty much entirely on the judgement of the officer).  So, FSBs are very helpful for the prosecution because they are effectively always inculpatory, since there's rarely a way to impeach the officer's testimony that the person failed.</p>

<p>Field breathalyzers are potentially unreliable, and in fact are inadmissible in some states (e.g. Kentucky, <a href="https://casetext.com/statute/kentucky-revised-statutes/title-16-motor-vehicles/chapter-189a-driving-under-the-influence/section-189a104-alcohol-or-substance-testing-subject-to-refusal-or-enhancement-ofpenalties-under-krs-chapter-189a" rel="nofollow noreferrer">KRS 189A.104</a>), where the chemical test must be performed at the police station. There are training and calibration issues involved with the field machines, which are overcome with the in-station trained staff and well-maintained machines. Part of this procedure is waiting 15 minutes to be sure there is no alcohol in the mouth. Additionally, the more sophisticated big machines can specifically measure ethanol, not just methyl group structure which may reflect the fact that you were just painting.
These factors weigh against using field breathalyzers: they are more challengeable.</p>
