What's the difference - why spend any more?

As with everything, there is an element of "get what you pay for" and particularly in the case of the Fuel Cell detectors, the majority of the extra cost is going towards a significantly more expensive and sophisticated sensor. 

With a Semi Conductor Breathalyzer, while the sensor is generally quite accurate around the two calibration points of 0.03% BAC and 0.10% BAC (UK limit 0.08%) the results can be less satisfactory outside of these ranges, and particularly so at lower levels below 0.03%.  Needless to say, manufacturers all quote their accuracy as a figure +/- (x)% at the 0.10% level, and while this is generally repeated at this level accuracy does diminish at other measuring points.

A Fuel Cell, on the other hand, measures evenly throughout the range, hence why they are the only types of sensor used for Police grade detectors.  Fortunately, while a Police standard detector (such as the Dräeger 6510) costs around £700 there are now several Fuel-Cell based Breathalyzers available at considerably less - the PT500 for instance is just £199 + VAT.

The other reason for the price difference is generally down to the sampling method.  To get an accurate reading you need an accurate and consistent sample, but whereas the Fuel-Cell type of Breathalyzers also measure exactly 1.7ltrs of air each time (and expel the remainder through an air valve) the semi conductor models use either time alone (say a 3 second blow) or combination of time and pressure. Provided you use the Breathalyzer regularly, always take an average of 3 readings and blow exactly the same each time then you will get a good comparison, but generally the more expensive detectors in the £80+ range have more sophisticated time and pressure sensors to ensure you get as good a result as possible every time.

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