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RFI In Breathalyzers

Radio Frequency Interference (RFI) in Breathalyzers

One of the dirty little secrets in DUI law enforcement is that breathalyzers are susceptible to error caused by radio frequency interference (RFI), sometimes called electromagnetic interference (EMI).  Put simply, any electronic device in the vicinity of the breathalyzer can emit electrical energy which can interfere with the circuitry of the machine, causing false test results.  (A common example of the problem can be found in restaurants, where signs saying “Warning: Microwave in Use” alert customers to the danger of radio frequency interference with heart pacemakers.) 

In February 1982, Smith & Wesson, a major manufacturer of DUI breath testing devices, notified law enforcement agencies that its Breathalyzer Model 1000 had been found to experience interference from radio frequency transmissions under certain DUI test conditions, resulting in false test results. Subsequent investigation suggested that various power levels also affected Breathalyzer accuracy in Models 900 and 900A.

The potential sources of radio frequency interference (RFI) within the law enforcement environment are numerous – for example, AM and FM radios, police station dispatchers, hand-held police transmitters, teletypes, and police radar units. Each of these may emit the kind of interference that could cause specific DUI breath alcohol test devices to render false results. It was then learned that the federal government (National Bureau of Standards) was testing for RFI sensitivity in every type of breath testing device currently in use by law enforcement agencies in DUI investigations.

On September 10, 1982, Smith & Wesson issued a customer advisory suggesting that all breathalyzers used in drunk driving investigations be tested as a matter of preparedness for possible courtroom testimony to avoid the issue of RFI in breathalyzers.

For more information about how this issue may impact your case, call The Law Offices Of Taylor & Taylor at (562) 330-4173 or fill out our online contact form.

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