Every breath analyzer falls into one of two camps based on its sensor: semiconductor (MOS) or electrochemical fuel cell. The choice determines accuracy, cost, lifespan and where the device belongs.
Semiconductor sensors are affordable and fast, making them ideal for personal use and high-volume preliminary screening where a pass/fail indication is enough. They are, however, more prone to interference from substances like acetone and need more frequent recalibration.
Fuel cell sensors react specifically to ethanol, delivering precise, repeatable readings that hold up as evidence. They cost more and are the right call for law enforcement, evidential testing and any situation where a number — not just a colour — decides someone's day.
How the two sensors actually differ
A semiconductor sensor is a heated metal-oxide film whose electrical resistance changes when a reducing gas settles on it. Ethanol is one such gas. So are acetone, methane, and a long list of solvents and cleaning products. The sensor reports that something reactive is present, and the device converts that into a number. It cannot tell you which compound caused it.
A fuel cell works on a different principle. Ethanol is oxidised at one electrode while oxygen is reduced at the other, and the current that flows between them is proportional to how much ethanol was in the sample. The chemistry is specific: compounds that are not ethanol produce little or no current, so the number means what it says.
That specificity is the whole difference. It is why a fuel cell reading survives a challenge and a semiconductor reading generally does not.
Where each one belongs
Semiconductor devices earn their place at the front of a process. Screening a queue of workers at a gate, checking a driver before a shift, a personal unit someone keeps in a glovebox — anywhere the question is "is there anything here at all" and a positive result leads to a second, better test rather than a consequence.
Fuel cell devices belong wherever the reading itself decides something. Roadside enforcement, a positive screen at a workplace, an incident investigation, anything that could end up in front of a court or a tribunal. If somebody may lose a licence or a job because of a number, that number has to come from a sensor that only responds to alcohol.
Cost, drift and lifespan
Semiconductor sensors are cheaper to make and cheaper to replace, but they drift faster and are more sensitive to heat, humidity and age. Calibrate them on schedule and they stay useful; skip it and they stay confident while quietly going wrong.
Fuel cells cost more up front and hold their calibration considerably longer. Across a device's working life the difference in running cost is much smaller than the difference in purchase price suggests — and on a unit used daily, the longer calibration interval is often what makes the total cheaper.
Neither sensor lasts forever. Both have a finite number of tests in them, and both need a documented calibration history if the readings are ever going to be relied on.
What to do about false positives
A semiconductor device flagging a worker who has had no alcohol is not necessarily faulty. Mouthwash, some medicines, residual solvent on the hands and a recent drink still in the mouth can all raise a reading. This is why a screening result should never be acted on directly.
The standard answer is a waiting period followed by a confirmatory test on a fuel cell device. Fifteen minutes with nothing taken by mouth clears residual alcohol from the mouth itself, and the second reading measures what is in the deep lung air — which is what actually reflects blood alcohol.
The practical answer
For most organisations the answer is not one or the other. It is semiconductor units for the first screen, where volume matters and cost per unit matters, and fuel cell units for confirmation, where accuracy matters and volume does not. AlcoBreath stocks both, and we will help you draw the line in the right place.