As a DUI Defense Attorney, we are looking for any manner to challenge the breath test. One is the presence of RFI. However, the government is constantly telling us it's not a problem. It doesn't affect the test. They just trying to cloud the issues. But the government knows better, and it is a problem.
While a bit dated, the NHTSA's Limited Electromagnetic Interference Testing of Evidential Breath Testers points out this concern.
The report stated that states should subject to their instruments to field testing to determine susceptibility. They recognize that the evidential breath testing devices may be adversely effected by RFI. That the RFI has a potential for inaccurate results.
How has this changed over the years, it's still present. The manufactures have improved the quality of the shielding, but it can still impact the result. I have observed a cell phone ringing during a test that increased the result at a training. It does happen.
Today with digital phones, mini-pocket computers, radio's on a digital wave length, not to mention all the other electronic data around the breath machine, we just don't know how bad it is. And we just don't know cannot be the mantra the government relies upon.