How Ignition Interlock Devices (IIDs) Function
An ignition interlock device (IID), or car breathalyzer, is a sophisticated system connected to a vehicle's ignition [1.7.5]. Before the engine can start, the driver must provide a breath sample into a handheld unit [1.7.4]. This unit uses a fuel cell sensor, which is highly accurate and specifically designed to detect ethanol, the type of alcohol found in beverages [1.7.3]. If the driver's Breath Alcohol Concentration (BrAC) is above a pre-set, low-level limit (typically between 0.02% and 0.025%), the IID will prevent the car from starting [1.4.1, 1.7.4].
To ensure continuous sobriety while driving, the devices also require periodic 'rolling retests' [1.7.4]. During these tests, the driver must provide another breath sample within a few minutes of being prompted by an alert [1.7.2]. If a rolling retest is failed or missed, the device logs a violation and may activate the car's horn and lights until the vehicle is turned off [1.7.5]. The device does not, however, shut down the engine while the car is in motion for safety reasons [1.7.5]. All test results, passes, fails, and any attempts to tamper with the unit are recorded and downloaded for review by monitoring authorities [1.7.3].
The Problem with Residual Mouth Alcohol
IIDs are designed to measure alcohol from deep lung air (alveolar air), which accurately reflects the alcohol content in your bloodstream [1.2.6]. However, the breath sample must first pass through your mouth. If you have recently used a product containing alcohol, the device can pick up the lingering alcohol residue in your mouth [1.2.6]. This is known as 'residual mouth alcohol.'
Many mouthwashes contain a high concentration of ethyl alcohol to act as a solvent and a sanitizing agent—some formulas contain between 14% and 27% alcohol [1.2.5]. Using such a product immediately before blowing into an IID can cause the device to register a positive result, even though you have not consumed an alcoholic beverage and are not impaired [1.2.1, 1.3.2]. This reading is often called a 'false positive' or a 'contaminated reading,' though technically the device is accurately detecting the presence of alcohol molecules [1.2.2].
Preventing an IID Failure from Mouthwash
The good news is that residual mouth alcohol from sources like mouthwash dissipates very quickly, usually within 10 to 20 minutes [1.3.1, 1.4.1]. This is because the alcohol has not been absorbed into your bloodstream. To avoid a test failure, you can take several simple precautions:
- Wait 15-20 Minutes: The most effective method is to simply wait at least 15 to 20 minutes after using an alcohol-based mouthwash before attempting to provide a breath sample [1.4.1].
- Rinse with Water: Vigorously rinsing your mouth with water after using mouthwash can help clear away the alcohol residue more quickly [1.2.2, 1.4.3]. It is a recommended practice to keep a bottle of water in your vehicle for this purpose and to rinse before every test [1.4.3].
- Switch to Alcohol-Free Mouthwash: The safest option is to use a non-alcoholic mouthwash [1.5.1]. Nearly every major brand offers an alcohol-free alternative that eliminates the risk of a mouth-alcohol-related test failure entirely [1.5.1].
Other Products That Can Trigger a Failed Test
Mouthwash is not the only common product that can lead to a positive IID reading. Many other household items contain trace amounts of alcohol that can cause a temporary failure if used shortly before a test. These include:
- Foods: Fermented foods, ripe fruits, bread products (due to yeast), and pastries like donuts or cinnamon rolls can produce trace amounts of alcohol [1.8.2, 1.8.4]. Dishes made with cooking wine or vanilla extract (which can be 35-40% alcohol) are also culprits [1.2.4, 1.8.3].
- Beverages: Energy drinks, some fruit juices, and fermented drinks like kombucha can contain small levels of alcohol [1.2.7, 1.8.2]. Even products labeled 'non-alcoholic' beer can have enough alcohol to be detected [1.4.1].
- Personal Care Products: In addition to mouthwash, breath sprays, perfumes, colognes, and alcohol-based hand sanitizers can trigger a device if the fumes are concentrated inside the vehicle [1.2.1, 1.6.3].
- Medications: Some liquid cold and cough medicines, as well as asthma inhalers, use alcohol as a solvent [1.6.2, 1.6.3].
| Feature | Alcohol-Based Mouthwash | Alcohol-Free Mouthwash |
|---|---|---|
| IID Risk | High potential for false positive [1.2.5] | No risk of alcohol-related failure [1.2.1] |
| Waiting Period | 15-20 minutes required before test [1.4.1] | No waiting period needed |
| Common Ingredients | Ethanol (14-27%) [1.2.5] | Cetylpyridinium chloride, essential oils [1.5.1] |
| Best For | Users without an IID | All IID users [1.5.1] |
What to Do If You Get a Failed Test
If you fail a test and believe it was caused by mouthwash or another substance, do not panic. The system is designed to account for these situations.
- Rinse and Wait: Immediately rinse your mouth thoroughly with water [1.2.3].
- Retest When Prompted: The IID will enter a short lockout period (often 5-15 minutes) before allowing a retest [1.3.2, 1.4.6]. The residual alcohol should have dissipated by this time.
- Pass the Retest: A successful second test with a clean sample will demonstrate that the initial failure was due to mouth alcohol, not systemic intoxication, and will allow you to start the vehicle [1.2.1].
- Document the Event: It's wise to make a note of what you consumed and when, in case your monitoring authority asks about the initial failed reading [1.4.4, 1.4.6]. If the issue persists, contact your IID provider for assistance [1.4.5].
Conclusion
So, can mouthwash set off interlock devices? Absolutely. The high ethanol content in many common mouthwashes can cause a temporary failed reading due to residual mouth alcohol. While this is not the same as being intoxicated, it can prevent you from starting your vehicle and may be recorded as a violation. The most reliable ways to prevent this are to wait at least 15 minutes after using alcohol-based products, rinse your mouth with water before every test, and, for complete peace of mind, switch to an alcohol-free mouthwash. By being mindful of the ingredients in everyday products, drivers can navigate their IID program successfully and avoid unnecessary complications.
For more information on IID standards, you can visit the NHTSA's page on Alcohol Ignition Interlocks.
