A Breathalyzer (or breathalyser) is a device used to estimate the blood alcohol content. Breath analyzers don´t directly measure blood alcohol content or concentration, which requires the analysis of a blood sample. Instead, they estimate it by measuring the amount of alcohol in one´s breath.

(Breathalyzer, 2017)

The automotive breathalyzer as an ignition interlock aims to save thousands of lives and governmental expenses in health accidents related with drunk drivers. People driving while intoxicated still cause about 13,000 deaths a year in the United States. And of the 1.4 million arrests made, one-third involve repeat offenders. The greatest potential of ignition interlocks is to reduce this recidivism.

(NyTimes, 2009)


As our mission for the Qualcomm-ITESM Smart Cities Competition we seek to develop new ideas and fully-functional prototypes using modern technologies, primary the Dragonboard 410c Hack Kit from Qualcomm technologies and the 96 Boards support community.



· Breathalyzer

· Dragonboard 410c

· Relay

· Alcohol

· Multimeter

· Programming

· Network

· Digital/Analog


· Signal


· Digital Breathalyzer (STEREN)

· Shield GSM compatible with Arduino

· Logic Level Bidirectional Converter

· Dragonboard 410c

· Grobe Smart Relay

· Wire gauge 14 and 18

· A car

Step 2:

First Step: The Breathalyzer

· Buy a breathalyzer

· Disarm the front cover and access the inner circuits

· Identify the buzzer’s anode and cathode by the use of a digital multimeter

· Weld a thin wire to the anode (+) of the buzzer

· Weld another thin wire to the negative pole of the battery box allocated in the inner part of the breathalyzer.

Step 3:

Second Step: Decoding the behavior of the Breathalyzer

Every breathalyzer is different, so there is not a code that works in all of them.

For our first prototype we used the Digital Breathalyzer Steren MED-160

In our case, we identified that a breath lecture could have two main cases, in the first one the person who presented the lecture have had no alcohol consumption so the breathalyzer showed a 0.00 % blood alcohol content (BAC) lecture, and in the second case, the person had drunk some alcohol and the display gave a 0.05 % (BAC).

After some observation we came up with a solution, we noted that the process of a lecture in a sober person was determined by three stages that ended and started with a beep of the buzzer. In the case of a sober person, there were four beeps in the process. The lecture of a drunk person was similar, it passed through the same steps, but the main difference was that the breathalyzer beeped more times after showing the lecture in the display.

We took advantage of that observation and developed a code that counted the beeps and sent a signal to a relay that controlled the ignition cycle of the engine of the car. If you can find another node of the circuit which gives an analog signal you could use.

Step 4:

Third Step: Relay and car ignition

After you programmed the code to determine either if the person has a high BAC or not, you must use an electric signal in order to turn on the engine or not. Through the use of relays we amplified the voltage obtained with the DragonBoard from 1.8 volts to 12v which is received by the coil of the spark plug. Obviously, it’s a negated signal, which means that if the person is drunk then the device won’t allow the person to drive. In the negative case (a person with low or null BAC) the device is expected to turn on the engine after the key has enabled the lights and electric sensors.

Step 5:

Fourth Step: Communicating with SMS and Email

After the Breathalyzer allows or not to turn on the engine, we programmed the Dragonboard to send a signal to the GSM microcontroller. This GSM microcontroller is in charge of the communication between the device and a cellphone SIM card, it´s recommended to preset the message to be sent to a close friend´s number or a close relative because they are supposed to be advised in case the person is drunk. We have also programmed the Dragonboard to send an email to the close relative to double the chances of reply to the event.


As reported by the New York Times newspaper ignition-interlock devices were able to reduce repeat drunk-driving offenses by 65 percent. The impact on the community would be huge, reducing drastically the number of drunk drivers in the community would save thousands of lives that also would result in saving expenses in health and health insurances. This new technology could also be used in monitoring the sleep, drug abuse and other health conditions of the truck drivers at freight companies, decreasing the probabilities of suffering a crash and resulting in a benefit for both, the driver and the company.


Cook, P.; Gearing, M.. (2009). The Breathalyzer Behind the Wheel. februay 26, 2017, de The New York Times Sitio web: http://www.nytimes.com/2009/08/31/opinion/31cook.html

Breathalyser.org. (2007). Breathalyzer. february 20, 2017, de Breathalyzer.org Sitio web: breathalyzer.org/id2.html

<p>Can you add more details on how the DragonBoard is used in this project?</p><p>I am guessing it runs the code that counts the number of beeps on the breathalyzer? can you post the links to source?</p>
many comercial breathalyzer nw have cameras to make sure the person driving is also the person being tested. its common to have a sober person blow into the machine and then the drunk person drive off.<br><br>Also there is an alcohol breath sensor for arduino that is probably easier to use than hacking a comercial made unit. you could juat start from scratch witn arduino and go from there.
<p>Nice design. Something like this in regular use could really save a lot of lives.</p>

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