Fuel cell vs semiconductor breathalysers: which should you trust?

Personal breathalysers range from $20 key-ring gadgets to devices costing well over $1,000. The biggest reason for the price gap isn’t the screen or the case. It’s the sensor inside, and there are two main types: semiconductor and fuel cell.

Semiconductor sensors

Semiconductor breathalysers use a small heated metal-oxide sensor. When alcohol in your breath touches the hot surface, the sensor’s electrical resistance changes, and the device turns that change into a reading.

They’re cheap to make, which is why they’re in almost every budget breathalyser. The trouble is that they’re not very selective:

They react to things other than alcohol. Cigarette smoke, some foods, and acetone on the breath can all affect the reading. Acetone is common in people with diabetes or anyone on a low-carb or fasting diet.
They drift quickly. Semiconductor sensors lose accuracy with use and age, often within months.
They’re sensitive to conditions. Temperature, humidity and how long the sensor has warmed up can all move the result.
They often read less accurately at the levels that matter. A device that’s roughly right at very high readings is no help if it’s wrong around the legal limit.

A semiconductor breathalyser can tell you whether you’ve been drinking. It’s much less useful for telling you whether you’re under 250 mcg.

Fuel cell sensors

Fuel cell breathalysers use an electrochemical sensor. Alcohol in your breath is oxidised on a platinum electrode, which produces a small electrical current. The more alcohol, the more current.

That reaction is specific to alcohol, which gives fuel cell devices some big advantages:

They’re alcohol-specific. Acetone and most other substances on your breath don’t trigger a false reading.
They’re accurate at low levels, which is exactly where you need accuracy when you’re deciding whether to drive.
They’re stable. Fuel cells drift far more slowly than semiconductor sensors and hold their accuracy for longer between calibrations.
They’re what the professionals use. Fuel cell technology is used in police roadside screening devices and in workplace and alcohol interlock testing.

The trade-off is cost. Fuel cell sensors are more expensive to make, so a good fuel cell breathalyser costs more than a semiconductor one.

Calibration matters for both

Every breathalyser sensor drifts over time, fuel cells included. The difference is how fast. A fuel cell device typically needs calibrating every 6 to 12 months, depending on how often you use it. We explain more in why calibration matters.

What to look for when you buy

A fuel cell sensor. If the listing doesn’t say “fuel cell” or “electrochemical”, assume it’s semiconductor.
Certification to a recognised standard. In Australia and New Zealand, AS 3547 is the standard for personal-use breath alcohol testing devices.
A way to get it calibrated. A device you can’t recalibrate is a device you’ll eventually have to throw away.
A local warranty and support. If something goes wrong, you want someone in New Zealand to call.

Why we only sell fuel cell devices

When your licence and your safety depend on a reading, a cheap sensor isn’t worth the risk. That’s why both of our devices are fuel cell based. Both are certified to AS 3547. The Alcofind AF-35C is an affordable device for everyday personal checks. The Lifeloc FC10 is a police-grade device built for frequent testing and a working life of 10+ years. Both can be recalibrated through our calibration service.

This article is general information. Breathalyser readings are a guide — if in doubt, don’t drive.