Abstract:
A method for preventing circumvention of a intoxication test includes defining a detection time envelope with a first sensor activated in response to the presence of a human test subject proximate the first sensor and sensing with a second sensor for a change from an ambient condition caused by the presence of the human test subject proximate the second sensor. The intoxication test is validated when a change from the ambient condition is detected by the second sensor during the time envelope defined by the first sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/781,748, filed Mar. 14, 2013, which is incorporated herein by reference for all purposes. 
    
    
     FIELD OF INVENTION 
     The present invention relates in general to sobriety testing techniques, and in particular to anti-circumvention apparatus and methods for use in sobriety testing systems. 
     BACKGROUND OF INVENTION 
     Sobriety testing, which includes testing for both alcohol and illegal drugs, has taken a prominent role in ensuring a safe and efficient society. For example, ignition interlocks on vehicles have proven their worth in preventing intoxicated drivers from entering the roadways and causing serious, including fatal, accidents. Sobriety testing has also allowed authorities, such as courts and law enforcement agencies, to monitor compliance with the court-ordered restrictions imposed on persons having committed an alcohol or drug related offense. Among other things, with the availability of reliable sobriety testing systems, such offenders can continue travel to work, school, or rehabilitation and thus contribute to society, rather than be a burden. 
     Attempts to circumvent these sobriety testing systems is significant problem. For example, an intoxicated driver might try to circumvent a breathalyzer-based vehicle sobriety interlock system by introducing air from an air compressor, compressed air canister, balloon, or other source of intoxicant-free air. And while a number of anti-circumvention techniques suitable for use in sobriety testing systems are known in the art, these techniques are subject to a number of significant limitations. For example, some known anti-circumvention techniques used with breathalyzer-based systems require that the person being tested manipulate the breath air flow into the test apparatus. In the blow-hum technique, the user starts with a normal blow of air, then switches to a blow of air combined with a hum. In the blow-suck technique, the user starts with a normal blow then quickly reverses to a suck or inhale. In the blow-blow technique, the user starts with a normal blow then changes to a harder blow or softer blow. 
     These air manipulation techniques are subject to some serious disadvantages. Among other things, they are difficult for the human test subject to master and require consistency and patience for even sober users to pass each time. Moreover, the blow-suck technique can be unhygienic. 
     SUMMARY OF INVENTION 
     According to one representative embodiment of the principles of the present invention, a method is disclosed for preventing circumvention of an intoxication test, which includes defining a detection time envelope with a first sensor activated in response to the presence of a human test subject proximate the first sensor. A second sensor senses for a change from an ambient condition caused by the presence of the human test subject proximate the second sensor. The intoxication test is validated when a change from the ambient condition is detected by the second sensor during the time envelope defined by the first sensor. 
     According to a particular embodiment of the inventive principles, the first sensor is a capacitive proximity sensor, which detects a change in capacitance caused by the presence of the human test subject in a surrounding detection field. In intoxication testing systems employing breath tests, the first sensor may also be a pressure sensor, which measures breath air pressure provided by the human test subject. In some embodiments, both a capacitive proximity sensor and a pressure sensor are used to define the detection time envelope. 
     In particular embodiments of the principles of the present invention, the second sensor is either an infrared thermometer measuring a temperature of the human test subject, a humidity sensor, a breath temperature sensor, or a combination of two or more of these sensors. 
     Embodiments of the present principles advantageously address the problems associated with the conventional breath manipulation techniques used to provide anti-circumvention protection in intoxication testing systems. In the case of breath testing systems, the need to master the blow-hum, blow-suck, and/or blow-blow techniques is substantially reduced or eliminated. Moreover, the principles of the present invention are applicable to a wide range of intoxication testing devices and systems with the potential for circumvention, including breath testing devices for vehicle interlock systems, stand alone breath testing devices, and similar devices and systems for alcohol and controlled substances. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a diagram of a portion of an interior of a vehicle including a sobriety interlock system suitable for demonstrating one possible application of the principles of the present invention; 
         FIG. 1B  is a high level functional block diagram of the exemplary sobriety interlock system utilized in the application shown in  FIG. 1A ; 
         FIG. 2  is a more detailed functional block diagram showing the primary subsystems of the handheld unit shown in  FIG. 1B ; 
         FIG. 3A  is an electrical schematic diagram of the humidity sensor shown in  FIG. 2 ; 
         FIG. 3B  is an electrical schematic diagram of the oral IR sensor shown in  FIG. 2 ; 
         FIG. 3C  is an electrical schematic diagram of the breath temperature sensor shown in  FIG. 2 ; 
         FIG. 3D  is an electrical schematic diagram of the face proximity sensor shown in  FIG. 2 ; 
         FIG. 4A  is a plan view diagram showing the outer surfaces front and back panels forming the case of the handheld unit shown in  FIG. 1A ; 
         FIG. 4B  is a plan view diagram showing the inner surface of front panel shown in  FIG. 4A , including the face sensor electrode shown in  FIG. 2 ; 
         FIG. 4C  is an exploded view of major structural components of the handheld unit shown in  FIG. 1A ; 
         FIG. 4D  is a plan view diagram showing one side of the printed circuit board of  FIG. 4C , including selected subsystems shown in  FIG. 2 ; 
         FIG. 4E  is a plan view diagram showing the opposite side of the printed circuit board of  FIG. 4C , including the oral IR sensor and the face proximity subsystem-to-electrode clip shown in  FIG. 2 ; and 
         FIG. 5  is a conceptual timing diagram illustrating an anti-circumvention method using multiple sensors according to one representative embodiment of the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The principles of the present invention and their advantages are best understood by referring to the illustrated embodiment depicted in  FIGS. 1-5  of the drawings, in which like numbers designate like parts. For discussion purposes, these principles will be described in conjunction with an alcohol breath testing system operating within an vehicle ignition interlock system. It should be recognized, however, that the anti-circumvention systems and methods described below are equally applicable to other types of sobriety testing systems, including stand-alone sobriety testing systems and those designed to test for other types of intoxicants and controlled substances (e.g., marijuana). 
       FIG. 1A  is a diagram showing a portion of the interior of a motor vehicle in the area of the dashboard. A handheld breath alcohol testing unit  100  is connected to electronic circuitry behind vehicle dashboard  101  (see  FIG. 1B ) through a cable  102 . Generally, a person attempting to start the vehicle must provide a breath sample to handheld unit  102 , which tests for deep-lung breath alcohol content, deep-lung alcohol content being directly proportional to blood alcohol concentration and thus intoxication level. If the person being tested passes the breath alcohol test, the interlock system allows the vehicle to start. On a test failure, the interlock system disables the vehicle ignition system and the vehicle is rendered inoperable. 
       FIG. 1B  is a high level functional block diagram of the overall interlock system. Handheld unit  100 , which is discussed in detail below, includes a substance sensor  103 , which in the illustrated embodiment is a fuel cell alcohol sensor, an interlock system controller  104 , a keypad  105  for data entry, and a display  106 . 
     Handheld unit  100  electrically communicates through cable  102  with electronics behind dashboard  101 , including interlock system memory  107  and vehicle electronics/electrical system  108 . Interlock system data memory  107 , which is preferably solid state memory, such as Flash memory, stores the results of tests performed by handheld unit  100  for periodic retrieval and review by authorities monitoring the driver for compliance with any conditions or restrictions imposed on the driver. While interlock system controller  104  is located within handheld unit  100  in the embodiment shown in  FIG. 1B , it may be located along with interlock data memory  107  behind dashboard  101  in alternate embodiments. 
     Vehicle electronics/electrical system  108  controls the operation of the vehicle in response to the outcome of a given test. As known in the art, the ignition system of a vehicle can be controlled in any one of a number of ways, including enabling or disabling relays providing power to the starter motor or sending enable or disable commands to one or more on-board computers. Vehicle electronics/electrical system  108  may also be used to generate visible or audible warnings in the event of a failed test, for example, causing the horn to sound or the headlights to flash. 
     A digital camera  109  or similar imaging device is also preferably provided to allow for positive identification of the person taking the breath test through handheld unit  100 . The images taken by digital camera  109  are preferably stored in interlock system data memory  107  for retrieval and review by the monitoring authorities. Advantageously, digital camera  109  reduces the possibility of a restricted or intoxicated driver of circumventing the interlock system by having a substitute person providing the breath sample to handheld unit  100 . 
     In one particular embodiment, handheld unit  100 , interlock system data memory  107 , vehicle electronics/electrical system  108  communicate, either in whole or in part, with the OBD-II diagnostic system standard on most motor vehicles. The OBD-II system provides an efficient mechanism by which monitoring authorities can access the data stored within interlock system data memory  107  through a standard OBD-II port and associated test equipment. In addition, the OBD-II also allows for vehicle operating data to be recorded and stored within interlock system data memory  107  for correlation with the results of sobriety testing performed through handheld unit  100 . 
     The OBD-II diagnostic system also provides a communications path for transmission of command and control signals from interlock system controller  104  to vehicle electronics/electrical system  108 . These command and control signals can be used by interlock system controller  104  to disable the vehicle in response to a failed intoxication test. 
       FIG. 2  is a more detailed functional block diagram of the primary subsystems within handheld unit  100  in a preferred embodiment of the principles of the present invention. In this embodiment, interlock system controller  104  is a Renesas RSF3650KDFB processor operating in conjunction with firmware stored in Flash memory  220 . For clarity, interface devices, such as the analog to digital converters (ADCs) interfacing the various blocks with controller  104 , and auxiliary subsystems, such has the fuel cell and grommet heaters, are not shown in  FIG. 2 . 
     A cylindrical grommet  200  receives a disposable mouthpiece  201  through an aperture  202  through the front panel of the case of handheld unit  100  (see  FIG. 4A ). Air introduced by a user (i.e., the human test subject) through mouthpiece  201  generally passes through cylindrical grommet  200  and passes out an aperture through the unit rear panel. 
     As air flow passes through grommet  200 , a set of at least one thermistor  203  and associated breath temperature measurement circuitry  204  measure breath temperature. As discussed further below, breath temperature is one parameter useful for detecting attempts to circumvent an alcohol breath test. 
     A pair of tubes  205   a - 205   b  tap the airflow through grommet  200  to a differential pressure sensor  206 , which measures breath pressure and breath air flow rate. As known in the art, in order for an alcohol breath test to be valid, the user must provide sufficient air pressure for a sufficiently long period of time to ensure that a deep-lung air is received by the alcohol sensor. If neither of these two conditions is met, interlock system controller  104  aborts the test and the breath test functional routine is reset. One device suitable for use as differential pressure sensor  206  in the embodiment of  FIG. 2  is a Sensormatic 35AL-L50D-3210 differential pressure transducer. 
     Once interlock system controller  104  determines that deep-lung air is being received, a pump  207  is activated to draw a sample of the air flowing through grommet  200  into a fuel cell  208 . In the illustrated embodiment, the air sample is drawn through tubes  209  and  210 . A pressure sensor  211  monitors the air pressure being provided by pump  207  through a tube  212 . One suitable fuel cell  208  is a Dart Sensors LTD 2-MS3 fuel cell operating in conjunction with a pump  207  available from PAS International, although other commercially available fuel cells and pumps may be used in alternative embodiments. A suitable device for pressure sensor  211  is a Sensormatic 33AL-L50D-3210 pressure transducer. 
     Fuel cell  207  implements a well-known electrochemical process to determine the breath alcohol content of the deep-lung air sample. From the air sample, interlock system controller  104  calculates the corresponding blood alcohol concentration and determines whether the user has passed or failed the test, depending on the legal limits imposed by the given jurisdiction. In response to the test result, interlock system controller  104  sends commands to vehicle electronics/electrical system  108  to enable or disable the vehicle ignition system. The results of the test are also recorded within interlock system data memory  107  for access by the monitoring authorities. 
     The user interacts with system controller  104  through keypad  105  and display  106 , which allow the user to receive prompts and initiate a test in anticipation of starting the vehicle. In addition, interlock system controller  104  may periodically require retest of the user to ensure driver sobriety after initial start of the vehicle. In alternate embodiments, a microphone  213  and speaker  214  allow for control of handheld unit  100  by voice command. 
     According to the principles of the present invention, multiple sensors are provided for preventing circumvention of the breath test. In addition to breath temperature circuitry  204 , handheld unit  100  also includes a humidity sensor  215 , an oral infrared (IR) sensor  216 , and a face proximity sensor  217 . In the embodiment shown in  FIG. 2 , face proximity sensor  217  operates in conjunction with an electrode  218  disposed on the inner surface of the front panel of the case of handheld unit  100  and at least partially surrounding aperture  202 . A clip  219  provides an electrical connection between the printed circuit board on which face proximity sensor circuit  217  resides and electrode  218  (see  FIG. 4E ). 
       FIG. 3A  is an electrical schematic diagram of a preferred embodiment of humidity sensor  215 . In the illustrated embodiment, humidity sensor  215  is based on a Honeywell HIH-5031-001 humidity sensor integrated circuit  300 , which measures relative humidity using a laser trimmed, thermoset polymer capacitive sensing element with on-chip integrated signal conditioning. Humidity sensor  215  measures changes in capacitance based upon increases or decreases in ambient humidity levels. Preferably, humidity sensor  215  is protected by a screen against condensation that can produce sensor saturation. 
     In the idle state, humidity sensor  215  measures the relative humidity and outputs a consistent voltage level. Human breath normally contains greater than 85% humidity. Hence, when human breath is introduced in the area surrounding humidity sensor  215 , the output voltage of humidity sensor  215  is expected to rise or fall from its initial reading at ambient. 
     In environments where the ambient relative humidity approaches that of human breath, detection of a change in relative humidity around the case of handheld unit  100  becomes more difficult. In particular, at humidity levels of 0 to 80%, the humidity sensor will respond with a detectable increase in output voltage level. However, at ambient humidity levels at or above 80%, the response curve of humidity sensor  215  flattens out, making any change due to the presence of human breath difficult or impossible to detect. In the case of high ambient humidity levels, human breath will cause the output from humidity sensor  215  to decrease. The output of humidity sensor  215  is either not used as the sole source of circumvention detection or simply discarded by interlock system processor  104  in the event that no measurable change in relative humidity over ambient is detected in the presence of human breath (i.e., the output response is flat). 
       FIG. 3B  is an electrical schematic diagram of a preferred embodiment of oral IR sensor  216 , which is based on a Melixis MLX90615 infrared thermometer integrated circuit  301 . Generally, an infrared thermometer reflects a beam off a target object to measure temperature and can be adjusted for the emissivity level of the intended target object. 
     In the preferred embodiment of handheld unit  100  shown in  FIG. 2 , the intended target of oral IR sensor  216  is the back of the throat of the user taking the breath test. In particular, the IR beam travels through a small relatively transparent window through the otherwise generally opaque body of mouthpiece  201 . The emissivity of the opaque body of mouthpiece  201  differs from the back of the human throat. Most of the IR beam passes through the window in mouthpiece  201  to measure the temperature at the back of the user&#39;s throat; however, enough of the IR beam is reflected by the opaque mouthpiece body to provide a sufficient ambient temperature reference voltage. (For circumvention detection, an accurate body temperature measurement is not required.) The differential between the ambient temperature and the temperature at the back of the user&#39;s throat is used as an indicator of a valid test. 
       FIG. 3C  is an electrical schematic of breath temperature circuitry  204  and associated thermistors  203 . Thermistors  203  are preferably glass encapsulated NTC thermistors that function on the principle of a proportionate resistive change versus measured temperature. As temperature increases resistance decreases, and vice versa. In other words, at lower temperatures, resistance will be high and at higher temperatures, resistance will be low. Breath temperature circuitry  204  constantly monitors the ambient temperature. As a breath sample is administered and air flows through grommet  200 , the change in temperature from ambient is continuously monitored and recorded as the resistance changes. 
     The breath passing across the thermistors  203  will either heat or cool the sensor. In cold ambient temperatures, the breath sample will increase the measured temperature. In warmer or hot ambient temperature ranges, the breath sample will decrease in measured temperature. (In ambient conditions that are close to body temperature, or approximately 37° C., it is possible there could be no change or a very slight change that may not be discernible. In this case, interlock system control processor  104  discards the breath temperature results) 
       FIG. 3D  is an electrical schematic diagram of face proximity sensor  217 . In the preferred embodiment, face proximity sensor  217  is based on an Atmel AT42QT1010 capacitive touch sensor integrated circuit  302 , which detects differences in capacitance when a human body approaches electrode  218  on case of handheld unit  100 . Specifically, electrode  218 , which is not grounded within handheld unit  100 , uses the inherent capacitance of the human body within the detection field to establish a return path to ground, which is detected by face proximity sensor  217 . 
     Advantageously, the face proximity sensor system is a non-mechanical contactless design and is not susceptible to temperature changes. However, since face proximity sensor  217  works by measuring small changes in capacitance, it can be sensitive to atmospheric changes, such as humidity. It is therefore critical to ensure that face proximity sensor  217  and associated circuitry are conformal coated. 
     To activate face proximity sensor  217 , the user places their lips around the base of mouthpiece  201  to be within the detection field. When triggered, face proximity sensor  217  provides a digital voltage output that is equal to the power supply voltage. The output level stays high as long as the sensor is triggered. This creates an envelope that can be used in a multiple sensor anti-circumvention technique discussed below. In the preferred embodiment, a logic 0 means the sensor is not active, and a logic 1 means the sensor is active and a human face has been detected. 
     The sensitivity of face proximity sensor  217  can be varied using capacitor C Sense . In an embodiment using the Atmel AT42QT1010 touch sensor integrated circuit  302 , the recommended range of values for capacitor C Sense  is 5 to 50 nF. Larger values for C Sense  generally increase the sensitivity, although too large a value can increase noise susceptibility and false triggers. In the preferred embodiment, a 0.033 uF value for capacitor C Sense  was found to provide a detection field in which the user only has to place their lips half way down mouthpiece  201 . Alternatively, with a value of the 0.022 uF, light contact to the base of mouthpiece  201  was needed to ensure triggering the sensor. 
     The Atmel AT42QT1010 device can, in some cases, get stuck in the enabled position (not the disabled). If this happens, the face proximity sensor  217  will automatically reset itself and return to the disabled position. If power to the face sensor chip  302  is provided from the programmable input/output pin of interlock system processor  104 , the system firmware can provide for faster reset and force recalibration. 
       FIG. 4A  provides views of front panel  400  and back panel  401  of the preferred plastic case of handheld unit  100 . Front panel  400  includes aperture  202  for receiving disposable mouthpiece  201  into grommet  200 , along with display  106  and keypad  105 . Back panel  401  includes an aperture  405  allowing air passing through grommet  200  to exit handheld unit  100 . 
       FIG. 4B  shows the inside surface of front panel  400 , including proximity detection electrode  218 , which extends around the periphery of aperture  202 . Preferably, the surface of electrode  218  is four times the thickness of plastic front panel  400 . 
       FIG. 4C  is an exploded view of handheld unit  100 , including printed circuit board (PCB)  402 , which supports the majority of the subsystems shown in  FIG. 2 . The back face of PCB  402  is shown in  FIG. 4D  and the front face of PCB  402  is shown in  FIG. 4E . (In  FIG. 4A , display  106  has been folded to the side to expose the front surface of PCB  402 ). As discussed above, PCB  402  is preferably conformal coated to protect face proximity sensor  217  from humidity and condensation. 
       FIG. 4E  particularly shows spring contact  219 , which contacts electrode  218 , as shown in  FIG. 4B , to provide the electrical connection to face proximity sensor  217 .  FIG. 4E  also shows oral IR sensor  216 , which extends through a corresponding aperture in front panel  400  of  FIG. 4A  to allow and IR beam sensing of the back of the user&#39;s throat. 
     According to the principles of the present invention, the set of sensors, including breath temperature sensor  204 , differential pressure sensor  206 , humidity sensor  215 , oral IR sensor  216 , and face proximity sensor  217  can be used in various combinations, depending on such factors as environmental conditions, to ensure that a human subject is providing air to handheld unit  100  (i.e., the breath sample is not being provided by a mechanical source, such as an air compressor, air canister, or balloon).  FIG. 5  provides an exemplary graphical representation of the sensor outputs over time and when they would be valid during the breath test. 
     As shown in  FIG. 5 , a detection envelope is established by the output of at least one of differential pressure sensor  206  and face proximity sensor  217 . At least one of humidity sensor  215 , oral IR sensor  216 , and breath temperature sensor  204  is then used during the detection envelope to detect transitional changes from ambient conditions. Depending on the ambient conditions, these transitional changes can be either positive going or negative going, as shown in  FIG. 5 . (In some cases, the response curve of the given humidity sensor  215 , oral IR sensor  216 , or breath temperature sensor  204  may be flat, in which case interlock system processor  104  may discard the sensor output). 
     In other words, during a valid test, pressure sensor  206  should show minimal change at its output and face proximity sensor  217  should provide a constant active output signal, which in the preferred embodiment, is a logic 1. At least one of the set of transitional sensors (humidity sensor  215 , oral IR sensor  216 , and breath temperature sensor  204 ) should show a change in output voltage during the detection envelope defined by pressure sensor  206  and/or face detector  217 . 
     Generally, the more sensors that can be used the more difficult the system becomes to defeat. However, as discussed above, under certain environmental conditions, humidity sensor  215 , oral IR sensor  216 , and breath temperature sensor  204  may not detect a change relative to ambient (i.e., the sensor output response is flat during the test because any change created by human proximity to the sensor results in little, if any change, in the sensed parameter relative to ambient.) In addition, one or more of the set of sensors could fail. In the case of a flat sensor response curve or a sensor failure, interlock system controller  104  preferably discards the output of that sensor in determining the validity of the test. If too many sensors fail to provide valid information for interlock system controller  104  to validate the test, a conventional validation function, such as a blow-hum test, can be initiated. 
     Table I provides exemplary test validation procedures in pseudo-code according to the principles of the present invention. These procedures are preferably executed by interlock system processor  104  in response to firmware and the sensor outputs. In the procedure shown in the left column, the detection envelope is established using both differential pressure sensor  206  and face proximity sensor  217  and the test is validated using a change in ambient detected by one of humidity sensor  215 , oral IR sensor  216 , and breath temperature sensor  204 . The procedure shown in the middle column is similar, with the exception that the test is validated when a change is detected in at least two of the oral temperature, humidity, and breath temperature parameters from ambient. The third column shows an exemplary procedure for determining whether the output from a given humidity sensor  215 , oral IR sensor  216 , or breath temperature sensor  204  is a valid and suitable for use for breath test validation. Various other combinations of sensor outputs can also be used according to the inventive principles. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Multi-sensor scheme requiring at 
                   
               
               
                 Multi-sensor Scheme - Simple 
                 least 2 sensors 
                   
               
               
                 (Blow-hum as fall back) 
                 (Blow-hum as fall back) 
                 Valid sensor check 
               
               
                   
               
             
             
               
                 While air pressure = positive. 
                 While air pressure = positive. 
                 Delta = record start value 
               
               
                 { 
                 { 
                 Record stop value 
               
               
                  While face sensor = positive 
                  While face sensor = positive 
                 If not equal 
               
               
                  { 
                  { 
                 And (or) 
               
               
                  If Oral IR = delta 
                  If Oral IR = delta 
                 Delta &gt;= x 
               
               
                  If humidity sensor = delta 
                 ++acv 
                 Sensor works and can be used. 
               
               
                  If breath temperature = delta 
                  If humidity sensor = delta 
                 rise or fall in start value 
               
               
                  Then Breath sample = valid 
                 ++acv 
                   
               
               
                  } 
                  If breath temperature = delta 
                   
               
               
                 } 
                 ++acv 
                   
               
               
                 Display results 
                  Then Breath sample = valid 
                   
               
               
                 Else 
                 ++acv 
                   
               
               
                 Abort test 
                  } 
                   
               
               
                 (or Else 
                 } 
                   
               
               
                 Display “abort test - use blow 
                 If acv &gt;= 2 
                   
               
               
                 hum” 
                 Display results 
                   
               
               
                 Force blow hum technique) 
                 Else 
                   
               
               
                   
                 Abort test 
                   
               
               
                   
                 (or Else 
                   
               
               
                   
                 Display “abort test - use blow 
                   
               
               
                   
                 hum” 
                   
               
               
                   
                 Force blow hum technique) 
               
               
                   
               
             
          
         
       
     
     In sum, the principles of the present invention provide circuits, systems, and methods for validating tests taken by a sobriety testing device or system. Advantageously, the difficulties associated with the conventional breath manipulation validation procedures, such as the blow-hum, blow-suck, and blow-blow techniques, are reduced or eliminated. (Although these techniques are still available for use, if necessary, as a backup.) While demonstrated in conjunction with a vehicle interlock system based on breath testing for alcohol with a fuel cell, these principles are equally applicable to other types of devices and systems that test for intoxication, including stand alone intoxication testers and devices for testing for other forms of controlled substances. 
     Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     It is therefore contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention.