California DMV enjoys a generous "rebuttable presumption of reliability" of DUI breath testing numbers.
But if the California DUI defense attorney shows a failure to follow - in any respect - any regulation or standard, the jury may give little weight to the number and at DMV, the burden of proof shifts to DMV to then prove the reliability of the test for DMV purposes.
Then when California DMV does not sufficiently meet the shifting of the burden, the DMV is required to take no action against one's California driving privileges.
All breath test manufacturers pretty much mandate the minimum 15 minute continuous observation period just prior to implied consent DUI testing.
This is codified in California Code of Regulation, Title 17, Section 1219.3 [Breath Collection]:
A breath sample shall be expired breath which is essentially alveolar in composition. The quantity of the breath sample shall be established by direct volumetric measurement. The breath sample shall be collected only after the subject has been under continuous observation for at least fifteen minutes prior to collection of the breath sample, during which time the subject must not have ingested alcoholic beverages or other fluids, regurgitated, vomited, eaten, or smoked.
Attorneys reasonably rely on California's case of Manriquez v. Gourley. A valid 15 minute continuous observation prior to a breath test, requires both:
(1) A California DUI officer shall remain in the presence of a breath test subject, and
(2) A California DU officer shall be able by the use of all his or her senses [(a) Sight, (b) Smell, and (c) Sound] to make the determination whether or not the breath test subject has ingested alcoholic beverages or other fluids, regurgitated, vomited, eaten, or smoked, or suffered physical symptoms (e.g. burped, belched or regurgitated gas) that could falsely elevate or in any way skew or affect the test numbers.
Lawyers concede the Manriquez case permits limited situations where the cop claims to do an observation during the transportation time to the breath test location, as long as both these things actually happen:
(A) the rearview mirror is tilted if backseat subject, and
(B) cop truly observed drunk driving arrestee with three senses during the driving time while transporting to the breath test place.
But when an Observing While Driivng Cop truly does A and B, upon parking the cop car, the cop exits and closes door; then walks around cop car (leaving arrestee alone in cop car). So the Bottom Line: Cop not truly able to use all senses prior to opening up DUI arrestee's door and then taking him or her in for the breath test.
[See Manriquez v. Gourley (2003) 105 Cal.App.4th 1227, 130 Cal.Rptr.2d 209]