A faulty breathalyzer used in almost 1,000 DUI cases in the last year by San Jose Police has led to a review by the Santa Clara County District Attorney’s Office that could result in hundreds of case rulings being overturned.

If the review finds that the device, the Alco-Sensor V, was the primary piece of evidence against a DUI suspect, it could result in a dropped case, said supervising Deputy District Attorney James Gibbons-Shapiro.

“We are in the business of fairness and justice,” Gibbons-Shapiro said. “We have to make sure we prosecute those people based on the most accurate information we have.”

The San Jose Police Department has arrested 865 people since it began using the device in November 2010, Gibbons-Shapiro said. In Palo Alto, the device was used to arrest 133 people since April 2010.

Both departments have stopped using the device.

As part of the review process, Gibbons-Shapiro said attorneys are examining cases from the date the police departments began using the device to determine in which of those cases the device was used as a primary screening device, and then they will identify attorneys and defendants involved in those cases.

Gibbons-Shapiro said he expects the review to be completed in about a month.

The matter came to the attention of the district attorney’s office after the office learned that authorities in Ventura County had found problems with the device.

The device registers an individual’s blood alcohol content by having him or her blow into it, and is administered in the field by an officer who suspects a driver is driving under the influence as part of other tests to test the individual’s mental acuity and physical dexterity.

Gibbons-Shapiro heads the district attorney’s misdemeanor cases team. He said the majority of the 7,000 DUI cases filed every year are misdemeanors.

The punishment for a first misdemeanor DUI conviction is usually a $2,000 fine and 48 hours of jail or community service, while four DUIs in 10 years and crashes resulting in injury or death constitute the bulk of felony cases.

“DUI cases are really, really dangerous, and they affect all of our safety,” Gibbons-Shapiro said. “The fact that we’ve had this setback is not going to change law enforcement’s vigilance in investigating these crimes and our vigilance in vigorously prosecuting them.”

He said that if the review reveals the device was the primary piece of evidence against those who have already served time, the district attorney’s office would clear their criminal and driving records.