The Intoxilyzer 8000 is an electronic instrument, and electronics are sensitive to radio energy. A breath test usually happens in a room full of transmitters: police radios, dispatch antennas, cell phones. Radio frequency interference is what happens when that energy reaches the machine’s circuits and moves the number.
Modern machines are built with an RFI detector that is supposed to sense interference and abort the test. The defense question is whether that safeguard did its job.
What RFI Is
Every radio transmitter sends out electromagnetic energy. When a transmitter is close to a sensitive electronic instrument, that energy can induce small stray currents in the instrument’s circuitry. In a breath machine, those stray currents can shift the reading. The effect was a serious problem with older instruments, and it is the reason machines now carry RFI detectors at all.
A breath test happens surrounded by transmitters. Their energy can reach the instrument and move the reading. The machine’s RFI detector is supposed to sense interference and stop the test, but only if it is working and only if it catches what is in the room.
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A breath reading at or above 0.08 also starts the 10-day license clock.
A breath result over the limit triggers an administrative suspension on top of the criminal case. You have 10 days from the arrest to demand a formal review hearing with the DHSMV in Clearwater, which protects your license and can secure a 42-day permit. We file that request the same day you hire us. Call or text (727) 761-4318.
The Detector Is the Safeguard
The Intoxilyzer 8000 has an RFI detector designed to sense interference and stop the test before it produces a bad result. When it works, the machine prints an RFI DETECT code and aborts the test rather than reporting a corrupted number. That safeguard only protects you if it was working and if it caught the interference present in the room. A detector that missed a transmission, or one that was not functioning, leaves the door open to a reading shaped by something other than your breath.
What We Look For
We look at the environment of your test and the machine’s records. Was the breath room full of active radios? Did the instrument log any interference? The agency inspection is supposed to confirm the machine can detect radio interference and then inhibit and report it, so we check that those tests were run and passed for the instrument that tested you. When the answers do not line up, the reliability of the result is fair to question. This sits close to the inspection and calibration records we already request.
Why This Matters in Your Case
RFI is not a guarantee that your number was wrong. It is a reason the State has to show the number was right, that the machine was shielded, the detector worked, and nothing in the room moved the result. When that showing is thin, the reading is open to challenge, and it pairs naturally with the margin of error.
Where Radio Frequency Interference Comes From
A breath instrument is a sensitive electronic device, and it sits in one of the most electronically noisy places imaginable: a police station. Handheld police radios, dispatch equipment, cell phones, and other electronics all emit radio energy that can couple into nearby circuitry. That stray energy can disturb the precise measurements the instrument is trying to make, and the concern is real enough that Florida’s rules require the machine to guard against it.
The instrument carries a detector that is supposed to sense radio interference and abort the test. Like any safeguard, it works only within its range and only if it is functioning.
The Detector and Its Limits
To address the risk, the instrument includes a radio frequency interference detector that is meant to sense a disturbance and stop the test rather than report a tainted number. The existence of that detector is an acknowledgment that interference can affect results. But a detector has a limited range and sensitivity, it has to be working, and it cannot rule out every form or source of interference. A test that was not aborted is not the same as a test free of interference.
The machine keeps a record of interference
When the detector does catch interference, the machine does not just react in the moment, it writes it down. An RFI Detect event is logged in the instrument’s electronic data with a time, and it aborts the affected sample. That record is worth pulling, because it lets the defense see interference events not only on your test but across the machine’s recent history. A single flagged event tells you the environment around that machine can trigger it. A pattern of them, over many tests, tells you something about where the machine sits and how often its surroundings interfere with it. None of that shows on the one-page affidavit, and all of it is in the electronic record for anyone who reads it. So the detector is a safeguard, and the log it leaves behind is a second, quieter source of proof.
Records We Request
We look at the instrument’s maintenance and inspection records, the function of the interference detector, and what electronic devices were near the machine during your test. Where the records are thin or the environment was noisy, radio frequency interference becomes one more reason to question the reliability of the reading, alongside the calibration records and the overall condition of the machine.
Radio-frequency interference is easy for the State to wave off and harder to dismiss once you read the machine’s own record of it. I look at whether the detector flagged interference on your test, and I pull the electronic data to see how often that machine has flagged it before, because a device that keeps meeting interference in its own environment is a device whose readings deserve a closer look. I know how this detector works and where it falls short, and I let the machine’s records, not the State’s summary, tell the story.
I started out as an Assistant Public Defender in Florida’s Thirteenth Judicial Circuit, in Tampa, and today I am one of six ACS-CHAL Forensic Lawyer-Scientists in Florida, with forensic training in how these instruments work. A breath result is an estimate produced by a machine, and I read its calibration history, its agreement checks, and the assumptions built into the number, so I can show a jury where it does not hold up. Learn more about my background.
Questions About Radio Frequency Interference
Can radio interference affect a breath test?
Yes. A breath machine is an electronic instrument, and nearby radio transmitters can induce stray currents that shift the reading. That is why modern machines include an RFI detector.
What is an RFI detector?
It is a feature built into the breath machine that senses radio frequency interference and is supposed to abort the test if interference is present, so a compromised reading is not reported.
Does the Intoxilyzer 8000 protect against RFI?
It includes an RFI detector designed to catch interference. Whether it was working, and whether it caught everything in the room, is what a defense examines.
How is an RFI issue challenged?
We look at the radios and devices present during your test, any interference the machine logged, and the maintenance records showing the detector was tested and functioning.
Does the breath machine record radio interference?
Yes. When the Intoxilyzer 8000 detects radio-frequency interference of sufficient strength, it flags the event as RFI Detect, aborts the affected sample, and logs it in its electronic data with a time. Those flags can be reviewed for your test and across the machine’s recent history, even when they do not appear on the one-page affidavit.
Related: the main breath test defense page, how we challenge a breath test, and the calibration and inspection records.
This page is general information, not legal advice, and it does not create an attorney-client relationship. Breath testing in Florida is governed by Fla. Stat. 316.1932 and 316.1934 and the Florida Administrative Code chapter 11D-8. Procedures and rules change, and every case turns on its own facts. Past results do not guarantee a similar outcome.
