Intoxilyzer Calibration & Accuracy Checks: What Employers Should Know

What is Intoxilyzer calibration, and why does it matter?

Calibration is the process of confirming an evidential breath testing device reads accurately against a known reference and adjusting it if it doesn't. On an Intoxilyzer, that means running the instrument against a certified wet-bath or dry-gas alcohol simulator solution of known concentration and comparing the printed result to the known value, within the instrument's stated tolerance. A device that reads high produces false or inflated confirmation results; a device that reads low can let an over-the-limit employee test clean. Either failure mode undermines the legal defensibility of every test the instrument produces until it's corrected, which is why calibration records — not just the instrument itself — are what a DOT auditor or defense attorney asks for first.

How often should an Intoxilyzer be calibrated?

Calibration interval is set by the manufacturer's specifications and by the employer's or state's testing program requirements, and instruments used for DOT confirmation testing must stay within their calibration cycle at all times to produce a valid result. In practice that means a documented external calibration check on a fixed schedule — commonly every 30 to 90 days depending on usage volume and program requirements — plus an internal accuracy check the instrument runs automatically as part of each test sequence. An instrument that fails either check gets pulled from service immediately, not used until the next scheduled calibration.

What happens during an accuracy check?

A technician runs the instrument through a full test sequence using a certified simulator solution at a known target concentration (commonly around 0.08), records the instrument's reading, and compares it against the certified value and the manufacturer's tolerance window. The check also verifies the instrument's air blank reads zero, its internal standard checks pass, the printer produces a complete and legible ticket, and the simulator solution itself is within its own expiration and lot-certification window — a stale simulator solution can fail an otherwise good instrument. The result, the simulator lot number, the technician, and the date all get logged, because that log is the paper trail that makes a confirmation test defensible.

Check	What's verified	Typical frequency
Internal accuracy check	Instrument's own reference standard vs. sample reading	Automatic, every test
External calibration check	Instrument reading vs. certified simulator solution	Every 30–90 days per program
Full calibration/service	Adjustment, printer, air pump, sensor performance	Per manufacturer schedule or after any failed check

Who can perform Intoxilyzer service and calibration?

Service and calibration on CMI Inc. Intoxilyzer instruments should be performed by a technician trained by CMI on that specific instrument line, using CMI-approved simulator solutions and procedures. Foster Special Instruments is an authorized distributor and service provider for CMI Intoxilyzer instruments in the U.S., with technicians trained directly by CMI — Foster is not sponsored or endorsed by CMI, but is trained and equipped to perform manufacturer-specified calibration and repair. Using an untrained technician or off-spec simulator solution is one of the more common ways a program's calibration records get challenged during a DOT audit or in litigation.

What does a Foster calibration visit actually look like?

A Foster field tech arrives with fresh, lot-certified simulator solutions rather than relying on whatever solution is already sitting at the customer site, since a stale solution is one of the fastest ways to fail an instrument that's actually fine. The tech runs the instrument through a full sequence at the target concentration, checks the air blank reads clean zero before and after, inspects the sample chamber and mouthpiece port for contamination, confirms the printer produces a legible, complete ticket with correct date and time, and logs the simulator lot number alongside the instrument's serial number on the service record. If the reading drifts outside tolerance, the tech adjusts the instrument on-site when the fix is within spec, or pulls the unit for CMI-level service and leaves the customer a loaner if one's needed to keep the program running.

What questions come up during a DOT compliance review?

Reviewers most often ask for the calibration log tied to the specific instrument serial number used on the day of a disputed test, not just a general "we calibrate regularly" statement. A gap in that log — a missed 30- or 90-day check, a simulator lot with no certificate of analysis on file, or a calibration record with no technician name attached — is the kind of finding that turns a routine review into a real problem. Employers who keep the calibration log matched to the instrument's actual test history, rather than as a separate binder nobody cross-references, close that gap before it's ever asked about.

Frequently Asked Questions

What happens if a calibration check fails?

The instrument is pulled from service immediately and cannot be used for testing until it passes recalibration or repair. Any tests run since the last passing check should be reviewed, since a failed calibration can call prior results into question.

Do simulator solutions expire?

Yes. Simulator solutions are certified to a specific concentration for a limited shelf life and lot, and a program should track expiration dates the same way it tracks calibration due dates.

Can an employer calibrate its own Intoxilyzer in-house?

Only with a technician trained on that device model and access to certified simulator solutions and reference equipment — most DOT-regulated employers contract this out to a trained service provider rather than build that capability internally.

Foster Special Instruments handles breath alcohol instrument calibration alongside BAT training for employers running DOT-compliant alcohol testing programs. See how screening and confirmation testing depends on a properly calibrated instrument.