Cellphones and other transmitting devices should be turned off within at least 30-35 feet of any California DUI breath test machine or California DUI Preliminary Alcohol Screening (PAS) breath test. Otherwise there exists the serious risk of frequency interference, causing one's California drunk driving breath test machine result to not be accurate.
There are a number of different cellular systems in use in California. In order of possible cellular interference, they are AMPS and D-Amps (analog), CDMA Code Division Multiple Access (digital) and TDMA Time Division Multiple Access (digital). Analog is obsolete technology but it is still being used.
TDMA is easily the worst as it can easily inflate readings on most California DUI breath test machines. The cellphone is transmitting SID signals (Signal Identification Data) at regular intervals to maintain communication with the nearest cellsite when not receiving cellphone messages.
Cellphone interference increases when receiving voice or text because it is then in two-way communication to verify handset identity. That exchange takes place before the phone even rings and if there is a CDMA/TDMA phone near to an in-use landline phone or e.g. a computer speaker system, one can often hear the reply pulses sent by the phone before it rings. This strong source of invasive Radio Frequency Interference (RFI) makes any California breath tests conducted under those circumstances extremely suspect and seriously questionable.
Radio Frequency Interference detectors are quite crude as they cannot detect at cellular frequencies or produce unreliable results. Even the more regarded Draeger 7110 MKIII C (a purportedly superior machine not even used by San Diego DUI police) can be affected as it will produce erroneous responses when a TDMA phone is operated nearby.
The RFI detector simply does not detect all Radio Frequency (RF), no matter what the power or frequency. Normal radio traffic or FM or AM radio does not set off the detector. There further may be a threshold level for power or frequencies at which the RF detector aborts the California DUI breath test.
There was a study by Digital Corporation, done for CMI, the maker of San Diego Police Department's Intoxilyzer machine. That study included various documents showing when the RF detector is essentially blind at various frequencies.
Undetected RF can be generated by internal components that are old or wearing out, such as the chopper wheel motor and the cooling fan motor.
RF has the potential for altering the accuracy of the machine. That is why the California DUI breath test manufacturers attempted to build detectors as part of its machines.
DUI Prosecution experts cannot produce valid studies to determine the sensitivity of the California DUI breath machine's RF detector. Studies show undetected RF actually artificially doubles the California DUI breath test machine's readout.
Accordingly, all cellular and other transmitting devices should clearly be switched off or in flight mode within at least 30-35 feet of any California DUI breath test machine. Otherwise, the California drunk driving breath test number is probably not reliable.
Consult a California DUI Attorney for assistance with this possible California drunk driving defense issue.