Personal Breathalyzers are mainly based
on semi-conductor sensors and are designed in principle for use by a single,
regular user. It is assumed that the user is a willing participant, ie.
they are by definition trying to get an accurate, consistent sample; they are
not trying to "fool" the machine in any way either by varying the way they blow,
using mouthwash or any other means to avoid an accurate reading. Provided the
user ensures that every time they use the device they blow in the same manner,
that they always take the average of 3 readings (ignoring any spurious results)
and, most importantly, use the device primarily to determine how long it takes
them to return to zero they can be a very effective and useful device.
With regular use the user will know roughly
what result to expect for a given consumption and will also therefore be aware
if the readings start to become unreliable. When testing someone else, the
person doing the testing has no idea what to expect as they are obviously
unaware of the consumption of the person being tested; they cannot therefore
know whether the device is giving an expected, or spurious, result.
Semi-Conductors can be very accurate around
their calibration points (usually 0.03% & 0.10% BAC) but outside of this can
start to vary by a greater degree. Again, for personal use in determining
how long it takes to return to zero this is not a problem, but it can make any
single specific reading less reliable. Samples are only measured based
upon a set time (& sometimes minimum pressure) but the actual volume can be
varied considerably should the user choose to do so.
Professional Breathalyzers
are
specifically designed for testing other people. They measure a volume sample
(usually 1.7ltrs) irrespective of how long or how hard a person blows, and are
based upon an ElectroChemical Fuel Cell rather than a semi conductor sensor.
These fuel cells give an accurate reading throughout their range and are largely
impervious to compounds other than alcohol. They are more consistent, and more
resistant to contamination by excess alcohol (for instance by a test taken too
soon after drinking) and to smoke particle contamination. In most circumstances
within the UK we would always recommend the use of a UK-certified device,
however these are a little more expensive than those available from elsewhere
and in some circumstances it may be sufficient to use a non-certified
Breathalyzer, but one that is nevertheless designed for testing "unwilling"
subjects!
