If a police officer takes a breathalyzer reading of someone, what kind of record proves to a court what the reading was? General US information and/or info about California are both appreciated.

  • At the least, his notebook.
    – Dale M
    Sep 10, 2015 at 7:33
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    Related: Who wins “my-word-against-yours?"
    – feetwet
    Sep 10, 2015 at 18:48
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    If you really want to throw a wrench into the works, then ask for the computer program that runs the breathalyzer machine. Most companies won't release it. I've never read about any that did release the software, even when subpoenaed. Once denied you can use it as a springboard to claim you were not able to mount an effective defense because the information was withheld.
    – jww
    Aug 18, 2019 at 4:53
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    @jww A similar tactic may work against speed radar. I know of one person who claimed that he requested the recent calibration tests of the radar gun used on him. When those were not produced, his ticket was dropped. Breathalyzers may need similar, periodic, tests. Sep 2, 2021 at 12:43

1 Answer 1


Different states vary on all of this stuff but many times the roadside breathalyzer is given to establish probable cause to arrest a driver. After that the driver is given another test on a computer-connected breath tester at the station (or wherever). It's these big testers that are usually used as the evidence and are the ones which are at the center of controversy in various states.

As @Dale M stated, for roadside tests the officer can write the results in a notebook, some breathalyzers have printers, and other are connected to a computer. Whatever the case, there is usually a process that officers go through to ensure this stuff is accurate and complete. A lot of it is departmental policy and would only be revealed if challenged in court or perhaps via an open data request. But again, this record is to show probable cause for the arrest and the trip to the bigger badder test which is fully computerized and documented and witnessed. (In at least one state (NC) you have the right to have a witness present when you are tested.)

EDIT: Oh, and if your plan is to challenge probable cause because the record-keeping on the roadside breathalyzer is mediocre, the cop can cite all sorts of other probable cause, like he saw you swerving, you were slurring your speech, he smelled alcohol, you failed the in-car test, and you failed the roadside walking, touching, dancing, singing test.

  • Yeah, chain of custody and preservation of evidence are drilled into police. For common matters like DUI they have protocols that have been thoroughly vetted and accepted by the courts.
    – feetwet
    Sep 10, 2015 at 20:14
  • In my case I was arrested on DIP after defending myself from someone advancing on me. I asked for a breathalyzer because I knew I wasn't drunk, but the officer told me some ridiculously high number and refused to show me the readout. I'm guessing he just lied to me about my BAC and didn't write anything down.
    – B T
    Sep 10, 2015 at 20:44
  • Btw, do you know anything specifically about California?
    – B T
    Sep 10, 2015 at 21:36
  • Different cops in different town and counties probably all do it differently depending on their devices.
    – jqning
    Sep 11, 2015 at 0:44

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