Cannabis Breathalyzer: How It Works and Its Legal Status

Cannabis breathalyzer: the short answer

A cannabis breathalyzer is a device that measures THC in exhaled breath. THC is the compound in marijuana that causes impairment. As of 2025, no cannabis breath test is approved for roadside or evidential use in any US state. Police use field sobriety tests, a Drug Recognition Expert (DRE) exam, and blood or oral fluid samples instead.

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What the device measures

Exhaled breath carries THC in aerosol particles, not as a gas. The particles come from the lungs and the airway lining. A cannabis breathalyzer collects a breath sample and pushes it through a sensor. Hound Labs uses an immunoassay and mass spectrometry. Cannabix Technologies uses FAIMS (Field Asymmetric Ion Mobility Spectrometry). Both report results in picograms per milliliter (pg/mL). One picogram is one trillionth of a gram.

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Detection window

Studies of Hound Labs devices found THC in breath at a median of about 1.5 hours after smoking. Most positive samples were collected within 3 hours of use. THC clears from breath faster than from blood, and far faster than from urine. A urine test can stay positive for weeks after use, and it does not show impairment.

Buy Cannabis Breathalyzer Online: A Comprehensive Buying Guide

Legal status in the US

States set driving rules for marijuana in three ways: per se limits, zero tolerance, and impairment-only.

• Per se limits name a THC number in whole blood. Colorado, Montana, Utah, Washington, and Illinois use 5 ng/mL. Illinois adds a 10 ng/mL limit for carboxy-THC.
• Nevada and Ohio use 2 ng/mL. Pennsylvania uses 1 ng/mL under its medical program.
• Several states, including Arizona and Virginia, use zero tolerance. Any detectable THC metabolite counts.
• Other states, including California and New York, use impairment only and allow an affirmative defense.

Laws change each session. Verify the current statute in your state.

Accuracy limits

THC blood levels do not track impairment. A daily smoker can carry a high THC level with no impairment. A person who smokes once can show impairment at a low level. The same problem applies to breath. A breath test shows recent use, not current impairment. Small studies, small sample sizes, and no standard cutoff add more uncertainty.

Alcohol breathalyzer vs cannabis breathalyzer

Alcohol breath tests rest on fixed science. The blood-to-breath ratio for ethanol is about 2100 to 1. NHTSA maintains the federal Conforming Products List of evidential breath alcohol devices. No cannabis device appears on that list.

Research and pilot programs

Colorado funded roadside pilot studies with oral fluid tests. Michigan, Indiana, and California ran trials of oral fluid and breath devices. Hound Labs published breath data in the Journal of Breath Research in 2020 and 2022. Cannabix reported FAIMS lab results. Most of this work used small groups of volunteers who smoked under supervision.

What this means for drivers

• Do not drive after using cannabis. Reaction time, lane position, and attention change.
• An officer can arrest on driving behavior and field sobriety tests, even with no breath device.
• Blood and oral fluid results are the evidence used in court today.
• A breath test result will not settle the question of impairment on its own.