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SAN FRANCISCO — The California Supreme Court warned Monday that if officers administering field tests to people suspected of driving under the influence of alcohol don’t follow the guidelines for administering them, the tests could eventually lose their reliability. 

The justices said police must closely follow rules governing use of breath test machines for the results to be admissible at trial and to ensure future results are reliable. 

“Compliance with the regulations ... guarantees ... quick and certain admission of evidence, eliminating laborious qualification, critical cross-examination, and the risk of exclusion,” Justice Janice Brown wrote for the unanimous court. “Furthermore, compliance will ensure that the tests retain their reliability, and thus their relevance and admissibility in the future.” 

The judgment stems from Steven Vaughn Williams’ 1997 arrest for driving under the influence. 

His lawyers tried to get the breath test results thrown out, saying the arresting officer did not conform to state requirements for administering the tests.