In short, police breathalyzers are considerably more accurate.
Police breathalysers have an accuracy of less than ±2%. Some personal breathalysers can be anywhere up to ±40%.
We can and do supply police-grade breathalyzers such as the Draeger 6820 to customers who require a high degree of accuracy and reliability for personal use, or simply want the best.
In recent years there has been a large number of personal breathalyzers introduced to the market. These devices generally make use of cheaper semi-conductor based sensors which estimate the concentration of the sample based upon one or two pre-calibrated points; typically 0.03% and 0.10% BAC. At these values they tend to be quite accurate, but away from their datum points the drift can be quite dramatic – anything up to 30-35% variance on cheaper models is not unusual. Semi-conductor breathalysers are dramatically cheaper; whereas a typical police breathalyzer costs upwards of £900, many semi-conductor devices sell for less than £50.