Frequently Asked Questions (FAQ) and other useful Breathalyzer info!

The way to get the most from your Personal Breathalyzer is to use it regularly and use it to monitor the change in your level of intoxication, rather than looking at a single specific reading.. Always wait at least 15 minutes after drinking or smoking (or you can damage the sensor) and then test yourself, trying to blow steadily and consistently (see sampling below) so that you blow the same each time. Take 3 tests, each approximately 2 minutes apart, and compare the readings; if one is substantially different to the other two, try once more. when you have three readings that are within a reasonable difference of each other, take an average and wait 30 minutes - then test again. Don't be surprised if the reading is not exactly the same every time - see Sampling, Sensors and Displays below) - carry on testing every 30 minutes until you get a zero reading.  You may well find that the reading initially INCREASES, between the first few tests and the next - this is because it is taking time for the alcohol to be absorbed into the blood stream from your stomach. You will also probably find that the level does not drop by the same amount every half hour - this is one of the main reasons you bought your detector, to see how YOUR body reacts and how long it takes to absorb the alcohol.  You can use the guide to UK limits below to get some idea of how your readings compare, but if you intend to drive - do NOT drink!

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Sampling Method
One of the biggest differences between Breathalysers is the way in which they sample your Breath. Professional, police-grade Breathalyzers such as the PT750 and UK-Approved Dräeger 6510 measure an exact volume of air each time they are used - usually 1.7 litres. They incorporate a flow meter to measure the air and a physical gate to divert excess air once the required sample has been taken. This means they can obtain accurate results every time irrespective of how the user blows.

In contrast, "Personal" Breathalysers have varying methods of regulating the sample taken - some better than others! The simplest is the "Blow on" sensor - Keychain style and the compact "handbag" types like the AL2500 all use this method, with a short sample of breath taken by blowing at the unit. The AL2500 has a vent at the top of the unit which the user blows through instead of onto but none are able to take a full sample of deep lung air, but as a result the user must expect a reasonably large margin error with such units.  The next "step up" is to make the user blow through a tube; this helps to regulate the rate of sample, and enables a better standard of measurement to be taken. The lower-priced units like the Slim and AlcoHawk Precision are all of this type while further up the range again units like the AlcoHawk Pro Digital incorporate a pressure sensor which ensures a minimum air flow is maintained during sampling (though none will limit the maximum sample that can be taken).  When used regularly by a single individual, who develops a consistent blow of around 1.5 litres of air, the "blow-through" types can obtain a reasonably good level of accuracy, however anyone considering using a Breathalyzer to test others should only really look at the PT500, PT750 or 6510 or similar in order to be certain that the sample is identical and reliable every time.

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Sensor Types
Traditionally Breathalyzers were all designed around a device called a Fuel Cell. These are relatively expensive to manufacture (often £200 or more just for the Fuel Cell) but are highly accurate and reliable over a wide range and Breathalyzers certified for evidential use (known in the US as EBT's) use these sensors. In order to produce a more economic device for personal and home use various semi-conductor based sensors have been developed, which use varying levels of software complexity to translate their readings into equivalent values such as BAC%, mg/l and Microgrammes.  These sensors are more susceptible to drift (where the values produced gradually vary as the unit gets older and is used more often), saturation/contamination (for example if the user has been smoking or drinking recently) and variations in temperature but for general home use, provided some margin for error is allowed by the user, can produce some perfectly acceptable results. Semi conductor based sensors also have a narrower range of sensitivity and are more complex to calibrate (see below) so for Employers or Enforcement agencies, who must have a reliable and consistent reading over the full range of use, only Fuel Cell, EBT-approved devices like the ACS J5 and Dräeger 6510 are going to produce the required levels of accuracy and reliability.

Users should also bear in mind that the accuracy of a particular sensor quoted in the specifications has been measured under strict laboratory conditions immediately following calibration. Due to the variations listed above, and particularly the limitations of sampling, it is unlikely that such specific accuracy is likely to be obtained on a repeatable basis by the user "in real life" and sensor saturation with alcohol, or contamination with smoke during a test, can quickly destabilise the sensor software and lead to unreliable results. Anyone using a "personal" Breathalyser should leave a substantial margin of error and take into account general factors such as what and when they've been drinking - you cannot rely solely on a Personal Alcohol Detector to determine your level of intoxication!

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Calibration
Many handheld breathalyzers sold to consumers use a silicon oxide sensor which are far more prone to contamination and interference from substances other than breath alcohol. The sensors require recalibration or replacement every six months. Higher end personal breathalyzers and professional-use breath alcohol testers use platinum fuel cell sensors. These too require recalibration but at less frequent intervals than semiconductor devices, usually once a year and they are far more robust when it comes to dealing with high concentrations, such as would be found (for instance) in a rehabilitation clinic. There are two methods of calibration - dry gas, and wet bath simulation and all Breathalyzers can only remain accurate for so long before they need to be "reset" - or calibrated - against a known benchmark concentration level of alcohol. Each method requires specialized equipment and factory trained technicians. It is not a procedure that can be conducted by untrained users or without the proper equipment. On the whole a personal detector will remain accurate  provided it is used properly, but once consecutive readings start to drift by an unacceptable degree then it will need to be recalibrated. Regular recalibration (roughly every 6 months) also helps ensure the sensor stays within calibration range; once outside this range, it cannot be reset.Some semiconductor models are designed to allow the sensor module to be replaced without the need to send the unit to a calibration lab however as replacing the sensor does not test the unit itself "in situ" this method is not as reliable as having the unit properly serviced by a trained technician.

Fuel Cell devices will generally "hold" their accuracy for longer, however because they are usually in use in an evidential environment most companies have them calibrated at least every six months. Dry gas calibration can only be carried out on Fuel Cell devices and is generally done at a single concentration level.  Fuel Cells have a much more linear detection range the semi-conductor based sensors and as such are able to "predict" accurately both lower and higher concentrations from a single calibration point. The advantage of dry gas calibration is that little or no expertise is required to operate the equipment, and large-scale operators such as the police are able to have their own in-house setup in order to regularly check and calibrate their detectors.  If the readings are not what you expect, first try re-testing on several occasions to see if blowing technique is an issue - see "how to use a personal Breathalyzer" and "sampling methods" above

Semi-conductor devices on the other hand are calibrated using wet-bath simulators, which is a device containing water, mixed with pure alcohol at a precise level and heated to an exact temperature. A minimum of two are required, and a Customs & Excise licence is required to purchase and store the materials.  Semi-conductors have a much narrower, and less linear, range than fuel cells and so are usually calibrated at two points - a "low" level and "high" level just above and below the expected key point of use - in the UK, either side of the drink drive limit of 0.08 BAC%. The software in the unit then compares these two fixed points from the air supplied by the wet bath simulator and uses them to forecast other readings up and down the range. The problem however is that it is relying on the software to predict the results, and the non-linear nature of the sensor means it can only do so to within certain limits, particularly at very high (more than 0.20 BAC%) or very low (less than 0.02 BAC%) levels.  For personal use, as a general indicator of changes in the level of intoxication, semi-conductor based Breathalyzers are very useful devices but users cannot put too much store by any one specific reading and must allow reasonable margin for error (see Sensor Information here). To have a Breathalyzer calibrated, see our order page here.

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Displays and Measurement Units - BAC%, mg/l, microgrammes, etc
There are three basic types of display; LED's that show a range of values (like the SafeDrive Keychain and CA1000) and either backlit LCD or Digital LED devices that produce a digital reading.  These displays generally show three digits, however if calibrated to display the results in BAC% one digit is always a zero (The UK limit is 0.08%, so even someone 5 times over the UK limit would still only register a reading of 0.40%). Alternative forms of measurement include mg/L (where the limit is 0.40), mg/100ml (limit 80mg - this is the measurement reference used by UK police until around 5 years ago) and Microgrammes (the current Police standard, where the UK limit is 35 microgrammes)

Most "Personal" Breathalyzers sold in the UK display their results in BAC%, which is the standard most commonly used in the US. The problem with this standard is that between zero and the drink-drive limit of 0.08, the unit only displays a change of 8 "steps" of 0.01%, and approximates the values in between. For example, 3 tests taken 2 minutes apart may produce sensor values of 0.045, 0.050, and 0.055 - but all would display as 0.05. On a unit displaying mg/100ml however, the full reading would be displayed in full as 045, 050 and 055 allowing the user to make a more informed decision. Bearing in mind the comments made above with regard to sampling, it also gives the user more feedback as to the consistency with which they are using the Breathalyzer.

Certain websites claim that their devices actually "read" a sample in BrAC - "Breath Alcohol Content". Clearly this is nonsense - every sensor merely outputs an electrical signal, which is then converted by the software in the unit to correspond to an accepted value of measurement. Whether that is BAC%, mg/L, mg/100ml or Microgrammes is irrelevant - different standards have been adopted by different countries and all are as valid as each other provided the device is used correctly and properly calibrated at the time.  It is the same as weighing an apple in grams, pounds, kilos, stones etc - the apple still weighs the same!

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UK & USA Breathalyzer Approval Standards, ASD's vs EBT's
In the UK, the Home Office ONLY approve devices for Police and Law Enforcement use and as yet only Fuel Cell, fixed-volume sampling devices like the 6510 have so far been approved.  |While a minimum standard for Personal Breathalyzers would be highly desirable at the moment nothing exists and as a result many devices sold on the UK market are little more than novelty items.

US FDA 510k Clearance
All breath alcohol testers sold to consumers in the United States are required to be certified by the Food and Drug Administration,[7] while those used by law enforcement must be approved by the Department of Transportation's National Highway Traffic Safety Administration. Manufacturers of over-the-counter consumer breathalyzers must submit an FDA 510(k) Premarket Clearance to demonstrate that the device to be marketed is at least as safe and effective, that is, substantially equivalent, to a legally marketed device (21 CFR 807.92(a) (3)) that is not subject to Premarket Approval (PMA). Submitters must compare their device to one or more similar legally marketed devices and make and support their substantial equivalency claims. It is important to appreciate however that the FDA Screening Tests do not test the ACCURACY of the device in ANY WAY WHATSOEVER - they only check to make sure they are "capable of detecting alcohol". And that doesn't mean they won't detect other substances, and report them as alcohol! The devices are cleared as "screeners" which means they have met the requirements used by the FDA for detecting the presence of alcohol in the breath, however Screener certification does not mean that the device can measure breath alcohol content accurately. Many breathalyzers cleared by the FDA are very inaccurate when it comes to BAC measurement and no semiconductor device has ever been approved for evidential use (see below) by any State Law Enforcement Agencies or the U.S. Department of Transportation. For personal use, certification does at least ensure a basic level of performance and as a pre-screener, backed up by an evidential-level tester, they certainly have a place in the workplace or clinical areas but their "results" must be treated with the scepticism applicable to a far cheaper device than a professional quality breathalyzer.

US DoT Breathalyzer Clearance - ASD's vs EBT's
Department of Transportation (DoT) approve two types - ASD's (Alcohol Screening Devices) and EBT's (Evidential Breath Testers). Again, only Fuel Cell devices have been approved in the US as EBT's, but there are a substantial number of semi-conductor based devices that have been approved as ASD's, including the AL5000, CA2000, AlcoMate Pro S etc.  Users must remember that the US DoT approval is only limited to their ability to detect the PRESENCE of alcohol. They are NOT assessed for their ability to accurately measure a specific alcohol LEVEL, in the way that an EBT is. They are expected to be used only for general screening, with anyone that indicates anything over zero being re-tested using a properly approved EBT.  This makes them a very useful "morning after" device for home use and for measuring the comparative rate that an individuals' body metabolites the alcohol but users must realise that something costing in the region of £50 - £100 is not going to reproduce the level of specific accuracy and reliability of an EBT costing £700 or more.

UK Drink Drive Limits
The legal limit for alcohol levels in the body while in control of a vehicle vary from country to country and can be defined by several different standards, the following of which are the most common:

• 9 microgrammes - as used by professional Breathalyzers such as the Dräeger 6510, XT & 7410

• 20 mg/100ml - as displayed by the AlcoHawk Pro, CA2000 Pro and AlcoScan 6000 Pro

• 0.09 mg/L - as displayed on the AL5000 Pro

• 0.02%BAC - used by the majority of "consumer" Breathalysers