All breath analyzers — regardless of quality — require regular calibration to maintain accuracy. Over time, sensor drift can cause readings to deviate from true values, leading to false positives or negatives.
Most professional-grade devices should be calibrated every 6 months or after 500 tests, whichever comes first. High-use devices in industrial or law enforcement settings may require more frequent calibration. Follow the interval your device's manufacturer specifies; it is the one that matches that particular sensor.
The calibration process involves exposing the device to a gas standard of known ethanol concentration and adjusting the device's output to match.
Why sensors drift
A sensor is a physical thing, and physical things change. Electrodes age, the electrolyte slowly degrades, and repeated exposure to alcohol gradually alters how much current a given concentration produces. None of this is a fault; it is the normal life of a working sensor.
What makes drift dangerous is that it is invisible from the outside. A drifted device does not display an error or behave erratically. It gives a precise, confident, repeatable reading that happens to be wrong — and it will keep doing that until somebody checks it against a known reference.
Calibration, verification and adjustment
Three words often used interchangeably that mean different things.
Verification is checking the device against a known standard and recording what it reads. It changes nothing.
Adjustment is correcting the device so its output matches the standard.
Calibration properly means the whole documented process: check, correct if needed, and record. The record is not paperwork around the work — it is the work, because a reading is only defensible if you can show what the device was doing at the time.
What a known standard means
Two methods are in general use. A wet bath simulator bubbles air through an alcohol-water solution held at a controlled temperature, producing a vapour of known concentration. A dry gas standard is a cylinder of ethanol in nitrogen, certified at a stated concentration.
Dry gas is the more practical option for most sites: nothing to mix, nothing to hold at temperature, and a certificate for each cylinder. Whichever is used, the standard should be traceable to a recognised reference, and the certificate should be kept with the calibration record.
Keeping the record
For a device whose readings may ever be questioned, keep for each calibration: the date, the device serial number, the standard used and its certificate reference, the reading before adjustment, the reading after, and who performed it.
That is the difference between a result you can stand behind and one you merely believe. In a dispute the question is never "was the device accurate" — it is "what can you show about the device on that day".
Between calibrations
A full calibration on schedule is the floor, not the whole job. Between them: store the device within its stated temperature range, keep mouthpieces sealed until use, do not leave it in a vehicle in summer heat, and run a verification check if it is dropped or exposed to something unusual.
If a device starts reading noticeably higher or lower than a second unit on the same person, treat that as a signal rather than a coincidence. Two devices disagreeing is usually one device telling you it needs attention.
AlcoBreath supplies NIST-traceable calibration standards compatible with our devices, and can advise on the right interval for how yours is actually used.