Vehicle Code 23247 governs ignition interlock device offenses, including tampering with the device, having someone else blow into it, or driving a vehicle without the required device. When a DUI sentence includes an interlock, these rules carry real consequences. I am Joel Brand, and here is how the statute works and how I defend a charge under it.
What the statute prohibits
Section 23247 sets out several related prohibitions tied to the ignition interlock device, the breath-test unit installed in a vehicle that prevents it from starting if alcohol is detected. The statute makes it unlawful to tamper with or attempt to circumvent the device, to ask or allow another person to blow into it in order to start the vehicle for the restricted driver, to knowingly provide that kind of help to a restricted driver, and for a person required to have an interlock to drive a vehicle that is not equipped with one. In short, it protects the integrity of the interlock requirement that courts and the DMV impose after a DUI.
Why it matters after a DUI
Ignition interlock devices have become a standard part of DUI consequences in California, both as a condition of a restricted license during a suspension and as a requirement following many convictions. Because so many people with a DUI are now subject to an interlock, a charge under 23247 frequently arises as a follow-on to the original case. A violation can jeopardize the restricted license that is keeping a person driving, extend the interlock period, and add a new criminal charge on top of the DUI consequences already in place.
Knowledge and intent are key
The most important defenses to a 23247 charge usually turn on knowledge and intent. The circumvention and assistance provisions require that the conduct was done knowingly and with the purpose of defeating the device. There are innocent explanations for many situations that can look like a violation: another person may have driven the car without realizing it was an interlock-restricted vehicle, a passenger may have blown into the device without understanding the rules, or a mechanical issue may have caused a reading that looked like tampering. Whether the prosecution can prove the required knowing, intentional conduct is frequently where these cases are won.
Device malfunctions and false readings
Interlock devices are not infallible. They can register false positives from residual mouth alcohol, certain foods, mouthwash, or other substances, and they can malfunction or be poorly calibrated. A reading that the monitoring company flags as a violation may have an innocent technical explanation rather than reflecting any attempt to drink and drive or to defeat the device. I obtain the device's data logs and maintenance and calibration records, because those records often show that what was reported as a violation was actually a device error or a benign cause.
The "driving without the device" charge
One common version of a 23247 charge is driving a vehicle that lacks the required interlock when you were obligated to have one. Defenses here can include whether the person actually knew of the requirement, whether the requirement was validly in effect at the time, and whether there was a genuine emergency or other circumstance. As with the suspended-license offenses, a proper notice and knowledge analysis matters, and I examine whether the obligation was clearly and validly imposed before accepting that a violation occurred.
The consequences of a violation
A 23247 violation can carry its own penalties and, just as significantly, can disrupt the arrangement that is allowing a person to drive at all. It can lead to revocation of a restricted license, an extension of the interlock requirement, and additional terms. Because the device is often the very thing keeping a client on the road during a suspension, protecting against an unfounded violation is about preserving their ability to work and live normally, not just avoiding a fine.
How these cases resolve
The realistic goals are to show that any flagged reading had an innocent or technical explanation, to defeat the knowledge or intent element where the conduct was not a deliberate circumvention, to verify that any interlock obligation was validly imposed and known, and to protect the restricted license the client depends on. Where the device data or the circumstances support an innocent explanation, the charge can be defeated or the violation cleared. As always, the outcome depends on the records and the facts, which I examine closely.
How monitoring reports become charges
It helps to understand how these cases typically start. The interlock provider records every breath sample, every failed start, every missed rolling retest, and every service visit, and it reports that data to the court or the DMV on a schedule. A pattern of flagged events, or a single serious one such as an apparent attempt to bypass the device, can generate a referral that becomes a 23247 charge or a violation proceeding. The key point is that these charges rest on machine-generated data interpreted by a monitoring company, and that data is not beyond challenge. Residual mouth alcohol from food or hygiene products, a failure to understand the rolling-retest requirement, or a simple device error can all produce entries that look damning in a report but have an innocent explanation. I scrutinize the underlying log rather than accepting the provider's characterization at face value, because the difference between a real circumvention and a benign reading is often buried in the raw data.
How it fits the larger picture
Interlock offenses under 23247 are a downstream consequence of a DUI, tied to the restricted-license and suspension scheme. They connect to the court-conviction suspension under Vehicle Code 13352 and the administrative per se process. See my top DUI defenses and the defenses guide.
Accused of an interlock violation? Let's talk.
Whether a flagged reading was really a violation, and whether your license can be protected, is exactly what I review against the device records. Use the free case analysis on this page, or call me directly at (888) 271-6644. I answer my own phone, 24/7.