RFI May Invalidate Breathalyzer Results

Filed under: DUI by Contributor @ November 15, 2012

A lesser-known DUI defense that attorneys may employ to challenge a breathalyzer result is that of Radio Frequency Interference (RFI). Countless items use RF technology, from cell phones to GPS devices to police radios. These devices emit an electromagnetic field (EMF) that can throw off the results of a breathalyzer test. It should be noted that RFI only affects the desktop breathalyzers found in police stations, not the portable breathalyzers that officers carry in their vehicles.

First introduced in the 1950’s, early breathalyzers were not susceptible to RFI. But in the 1980’s, breathalyzers started using internal amplifiers as part of the technology that read a driver’s blood alcohol content (BAC). Unbeknownst to the breathalyzer manufactures and the police, the new equipment and the amplifiers inside were susceptible to RFI, which could give an inaccurate reading. A false reading could occur when an officer sent or received a radio transmission during the measurement process, as the EMF would alter the reading. In 1983, the National Bureau of Standards developed a report on the problem, calling it a “severe” issue. As a result, breathalyzers soon were equipped with lead shielding. This was shown to be ineffective, and now most breathalyzers have RFI detectors, lessening the chance that RFI can occur.

Even with these detectors, RFI can still occur. The detectors are only as reliable as the people who calibrated them. To be officially calibrated, a police department must send the device to the manufacturer, which many police departments are unwilling to do. Instead, a police officer will typically stand next to the detector and hold a police radio to it. If the detector shows RFI, then it is calibrated. The problem is that RFI detectors are essentially blind to certain bands on the electromagnetic spectrum, and police radios only use certain frequencies. A cell phone or other device could easily cause interference without the detector picking up on it.

Because of the possibility of RFI, DUI attorneys should be aware of this issue and raise it on cross-examination. A defendant may be able to win the case if the detector on the breathalyzer was not calibrated correctly.

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