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Alco-Sensor FST Approved Screening Device

The Alco-Sensor FST is now the only Approved Screening Device (ASD) regularly used in British Columbia. It was introduced in BC in January 2015 to replace the often-malfunctioning Alco-Sensor IV DWF Screener after we publicized internal police documents showing they were unreliable.

The Alco-Sensor FST is 12 cm tall with a grey plastic body. Typically it will have either a yellow or blue latex cover over the body and bezel. It weighs approximately 220 grams. The power source is two AA batteries with which it is capable of conducting more than 1000 tests.

The display is a backlit liquid crystal screen. In normal operating mode when a suitable sample is obtained the display will show Fail, Warn or the BAC under 60 mg%. It is not possible for police officers to determine the specific BAC using this device, unless the sample is less than 60 mg%.

The normal background colour of the screen is green when lit. If the reading obtained is Warn, the background colour will change to amber. If the reading obtained is Fail, the background will change to red.


The manufacturer recommends that it not be stored at temperatures colder than -15°C or hotter than 50°C. The manufacturer recommends that the device be programmed for use between -10°C and 50°C. The software in the devices now used in British Columbia are programmed to accept a sample at internal temperatures between -12 °C and 55 °C. The internal temperature is measured by a thermometer next to the fuel cell. If the device is outside of this temperature range, an error message will briefly appear and the unit will shut itself off. When functioning properly the Alco-Sensor FST will not accept a sample outside of this temperature range.


The Alco-Sensor FST has two buttons activated by the index finger and the thumb. The button on the front powers up the unit. The unit beeps once upon power up and the unit temperature is briefly displayed. On the top of the screen is a bar indicating the strength of the batteries.

Unlike previous ASD models, the Alco-Sensor FST model used in BC conducts an air-blank test by pulling in a sample of air and testing to ensure that the fuel cell is not contaminated by ambient alcohol or residual alcohol in the unit. There is a margin of error granted in the programming. If a small amount of alcohol is detected, the Alco-Sensor FST will still proceed to indicate that no alcohol was detected in the blank test.

After completing the blank test, the Alco-Sensor FST will indicate that it is prepared to accept a breath sample. The subject then is to provide a breath sample by blowing into the mouthpiece. The device will remain prepared to accept a sample for 3 minutes, after which it will shut itself off. The subject can attempt to blow three times within one testing sequence. Test results are displayed for approximately 10 seconds. There is no record created of the test results.

Air flow

If functioning properly, the Alco-Sensor FST will automatically accept a sample. A pressure sensor monitors the breath flow. When a certain volume of expired breath has been blown through it, a solenoid engages, activating a pump which pulls in a sample of breath from the mouthpiece.

The Alco-Sensor FST requires a minimum flow rate. If this is not met, the device will not detect the air passing through it. The Alco-Senor FST requires a minimum volume of air before it will automatically capture a sample. This volume must be achieved and then followed by a reduction in flow rate. The rationale for this is that such a reduction will signal to the device that it is testing deep lung air. By reducing the flow rate before deep lung air is expelled, the reading may be artificially reduced.

Testing and Calibration

In BC, the current recommendation is to use a dry-gas standard with a nominal target value of 82 mg% to conduct calibration checks on the Alco-Sensor FST. If the device is found to be outside of accepted parameters, it is then to be re-calibrated using a wet-bath alcohol standard with a target value of 100 mg%.

Both dry and wet bath alcohol standards have strict requirements for use that are not always followed. They must be used at specific temperatures, and must not be used past their expiry dates. Wet-bath standards can only be used for a maximum of two weeks or sixteen calibration checks, whichever comes first. If the use of a bottle of simulator solution exceeds this period, any recalibration done of the device may be unreliable. Small variations in temperature may cause the simulator to provide inaccurate readings causing inaccurate calibration.

The recommendation is that each Alco-Sensor FST be serviced on an annual basis. Calibration checks are currently done monthly. The fuel cells have a limited life and are often replaced during annual service. Blowing tobacco smoke into an Alco-Sensor FST will cause irreparable damage to the fuel cell. Blowing fresh alcohol directly onto the fuel cell may also cause irreparable damage. In either case there is no feature in the Alco-Sensor FST to alert the operator that the fuel cell has been damaged.

Because the Alco-Sensor FST is a hand-held device, it is susceptible to damage from dropping, transportation, travel, and frequent handling.

In our library of records we have calibration documents and service records for many of the Alco-Sensor FST units currently in service.

Mouth Alcohol and the Alco-Sensor FST

Unlike the breathalyzers at a police detachment which use infrared refraction to approximate breath-alcohol content, the Alco-Sensor FST is a fuel cell device. It uses two electrodes that react with the alcohol condensed on their surface. This is converted into an electronic signal that is then interpreted by the internal software. The result is then displayed.

The Alco-Sensor FST is lacking a slope detector, CO2 sensor or any other feature to determine whether the sample is contaminated by mouth alcohol. Studies have shown that mouth-alcohol contamination can take place as long as 40 minutes following the last drink or introduction of alcohol to the mouth. Although the Alco-Sensor FST is claimed to be specific to alcohol, we have located no peer reviewed studies to support this claim. Moreover there are different type of alcohol and other organic chemicals with similar properties to alcohol that may react to the fuel cell. There is evidence that the fuel cell devices cannot distinguish some other forms of alcohol, although some of the more sophisticated breathalyzers have this capability.

Issues of concern with the Alco-Sensor FST

The Alco-Sensor FST is a generally reliable and relatively sophisticated device but it also has significant drawbacks. It operates using three distinct systems all of which may malfunction on their own or in tandem. The electronic components, like any electronic components, can be defective or malfunction. The sample is obtained by a mechanical pump that can malfunction or be defective due to manufacturing error. The fuel cell relies on a consistent chemical reaction. A malfunction or defect in the fuel cell can cause inaccurate breath test readings. The electronic and mechanical components, as well as the fuel cell can be damaged by rough handling. The fuel cell can be damaged by cigarette smoke or even too much alcohol.

In addition, the Alco-Sensor FST uses complex software programmed into the EPROM chip. The software can be corrupted. The chip itself can malfunction.

It is subject to the same weaknesses as infrared breathalysers, including breath temperature, breathing patterns, incompatible partition ratio and malfunctions. In addition, it tests a smaller subject sample than previous ASDs used in BC, creating a risk of greater inaccuracy.

Further information about the Alco-Sensor FST?

A year before the police introduced the Alco-Sensor FST to British Columbia, we purchased a number of them for our lawyers to test and to perform certain experiments. We provide this information for the use of our clients and others who are trying to understand the weaknesses and strengths of roadside breath testing to determine blood-alcohol concentration. If you need assistance with an Immediate Roadside Prohibition or DUI case of any sort in British Columbia, please telephone us and we’d be happy to speak with you.

Call us for a free consultation and learn how we can successfully defend your IRP, ADP or drinking/driving charge.

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