Does Coffee Set Off Interlock Devices?

I am a coffee lover, and like many others, I start my day with a delicious cup of coffee. It gives me a boost of energy and helps me tackle the day’s tasks with enthusiasm. However, I recently discovered that there might be some unexpected consequences to my beloved morning ritual. There are claims that coffee can set off interlock devices. This got me wondering, is there any truth to this statement? In this article, we will explore the relationship between coffee and interlock devices and try to separate fact from fiction.

What are Interlock Devices?

Before we dive into the topic at hand, let’s first understand what interlock devices are. Interlock devices, also known as ignition interlock systems, are breathalyzer devices that are installed in the vehicles of individuals convicted of driving under the influence (DUI) offenses. These devices work by measuring the driver’s blood alcohol concentration (BAC) before allowing the engine to start. If the BAC is above the pre-set limit, the vehicle will not start.

How do Interlock Devices Work?

Interlock devices operate by analyzing the breath sample provided by the driver. The driver must blow into a mouthpiece attached to the device, which then measures the BAC level in the breath. If the BAC is below the set limit, typically 0.02%, the vehicle will start. However, if the BAC is above the limit, the vehicle will not start, and the event will be recorded in the device’s memory.

Can Coffee Set Off Interlock Devices?

Now that we understand what interlock devices are and how they work, let’s address the main question – can coffee set off interlock devices? The answer is no. Coffee, by itself, does not contain alcohol, which is the substance these devices are designed to detect. It is important to note that interlock devices do not detect caffeine or any other non-alcoholic substance. Therefore, consuming coffee should not trigger the device to prevent your vehicle from starting.

What about Coffee with Alcohol?

While coffee alone cannot activate interlock devices, what happens when we combine it with alcohol? Coffee is often consumed with alcoholic beverages, such as Irish coffee or spiked lattes. In these cases, it is essential to be mindful of the alcohol content of the drink. If the drink contains enough alcohol to surpass the interlock device’s set limit, it may indeed prevent the vehicle from starting. It is crucial to comply with the set limits and avoid driving after consuming alcoholic beverages, regardless of whether they are combined with coffee or not.

Other Factors to Consider

While coffee itself won’t set off interlock devices, there are other factors that may affect the accuracy of the results. It is crucial to be aware of these factors to ensure the device functions correctly and provides accurate measurements.

Mouth Alcohol Contamination

One common issue with breathalyzer devices is mouth alcohol contamination. This occurs when alcohol residue is present in the mouth, such as from recent consumption of alcoholic beverages or using mouthwash containing alcohol. When this happens, the device may mistakenly detect alcohol in the breath sample, leading to false-positive results. To minimize the risk of mouth alcohol contamination, it is best to rinse your mouth out with water before providing a breath sample.

Mouthwash and Breath Sprays

Some mouthwashes and breath sprays contain alcohol, which can interfere with the accuracy of interlock devices. It is essential to read the labels of these products carefully and choose alcohol-free alternatives if you are required to use an interlock device. Opting for alcohol-free mouthwash and breath sprays will help prevent any potential issues with false-positive results.

Residual Alcohol in Clothing or Environment

Another factor to consider is the presence of residual alcohol in your clothing or the surrounding environment. If you are in an environment where there is a significant concentration of alcohol vapor in the air, it may be detected by the device. Additionally, if you spill an alcoholic beverage on your clothing and the alcohol evaporates, it could still be detected by the device when providing a breath sample. It is vital to be mindful of these factors and avoid potential contamination.

Device Calibration and Maintenance

Interlock devices require regular calibration and maintenance to ensure accurate readings. It is crucial to follow the manufacturer’s instructions regarding maintenance schedules and any recommended actions. If your device is not properly calibrated or maintained, it may result in inaccurate readings, which can have serious legal consequences.


In conclusion, coffee by itself does not set off interlock devices. These devices are designed to detect alcohol, and coffee does not contain alcohol. However, it is important to be aware of the potential impact of combining coffee with alcoholic beverages. If an alcoholic drink exceeds the interlock device’s set limit, it may prevent your vehicle from starting. Additionally, other factors such as mouth alcohol contamination and residual alcohol in the mouth, clothing, or environment can affect the accuracy of the device. By understanding these factors and taking appropriate precautions, you can ensure the device functions correctly, providing accurate results, and promote safe driving practices. So, enjoy your cup of coffee, but always drink responsibly and drive safely.

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