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Breathalyzer ignition locks ? Answered


I know that in the USA these are used for drunken drivers. ( I think I saw it on '" My name is Earl.".)

Yesterday, listening to the radio, I heard a a UK politician propose that all new cars be fitted with these devices.

It made me think;  could a balloon filled with sober air be used to fool the machine ?

Does anyone in the industry know ?; If so, it would seem a very simple loophole.

Thank you.

This is a fine example of a failed test.


I am glad you are thinking about these things, about security systems (also called insecurity systems) and how these can be hacked.

You ask, "Does anyone in the industry know?"  Presumably someone does, but you don't have to be an insider (I'm not) to learn a little bit more about how certain technologies work.

Step 1:  Know your enemy ( or try to learn more about your enemy)

Wikipedia and Google are a good place to start, if you do not yet know anything about the system you want to hack.  So I appreciate the link to the Wikipedia article.  The next thing I wanted to know is, "who is it that is manufacturing these things"


And that search led me to this company. I am guessing it is one of the big ones.

Step 2: Product Literature and Videos
Just looking over the pages at SmartStartInc's web site, I notice a some things that are similar to something I read in the comments here.  Specifically those web pages mention some kind of "humming" technique required to unlock the device, and this seems similar to the Thematthatter's claim that the device is "programmed to the frequency of your voice, you have to hum into it..."

Step 3: Beware of Folklore
The word "legend" is used by folklorists to refer to a story which is believed, by some, to be true. In the vernacular, a false story, believed to be true, is called a "myth", although folklorists hate it when people do that, because to folklorists the word "myth" has a special completely different meaning, not just a false legend.

Throughout this journey of learning more about a particular insecurity system, you should be aware that some of the stories told about the system are true, and others are false, and others contain mixed amounts of truth and falsehood.

It is in the interest of the company selling the security device to promulgate legends about how smart, and sophisticated, and unhackable, or "fool proof" their system is. Also legends that exaggerate the capabilities of the system may get started on their own, just because stories that are remarkable/unbelievable are more memorable than stories that are boring.

For example, Thematthatter's claim the device is "programmed to the frequency of your voice", is probably false.  However the part about humming into the device to make it work is true, and that claim can be verified just from the documentation and videos from smartstartinc.com. 

As another example, consider this blurb from smartstartinc.com, about their optional camera module  (from http://www.smartstartinc.com/index.php/products/20-20)

By using the Photo ID module, Smart Start is able to positively identify the user of the device and minimize tampering, since a picture is being recorded. The device has several tamper detection features to prevent the user from covering the camera with tape or disconnecting it. When tampering is detected, the unit will send a message to the interlock aborting the test, thus preventing the user from starting the vehicle.

Is the device, the SSI-20/20, actually capable of recognizing human faces?  My guess would be no. Rather the device is capable of taking and storing pictures, and capable also of telling when its camera is blocked completely, but the actual image processing involved in figuring out who is blowing into the tube, is done offline, when the system is returned for its periodic maintenance appointments. Also guessing that offline processing is an actual human looking at the pictures.  Although, who knows?  Offline they ?might? have unlimited computing power to throw at the problem.  Or more likely they just hire some unlucky human eyeballs to look at the pictures.

Step 4: Search for patents
Patents can be full of juicy information, so while reading the company documentation be watchful for bragging about patents, if you are lucky, they'll just tell you the patent numbers.  If not, more searching is required.  For SmartStartInc's gizmos, I found these relevant patents: US6853956,US6167746,US6026674,US6956484

Step 4: Read the Patents
This part can be annoying, since patents can be voluminous, and full of, how do you say, TLDR. So its helpful to just give them a cursory glance, and sometimes interesting stuff will pop out. 

For example, in Figure 5 of US6167746, there is a flowchart showing three paths that can cause this breathalyzer to abort.  These are tests for breath pressure, breath temperature, and voice (which refers to the "hum" test mentioned previously)
Also this blurb, from the same patent, is a good summary:

"When used in an interlock device, the invention may incorporate additional elements and features to prevent an intoxicated person from defeating the interlock by introducing a sample from a source other than the operator's breath. The device may include a temperature sensor which will prohibit enablement of the machine unless the breath flow is within an acceptable range around human body temperature. The device may also incorporate logic within the computing device to prohibit enablement of the machine unless a pressure oscillation within the breath flow is detected. In the proper operation, the operator generates the pressure oscillation by humming while breathing into the device. The device may also enforce minimum and maximum blow-pressure limits to prevent the use of artificial samples and to detect the use of alcohol-removing filter media, such as activated charcoal, by detecting the resultant low pressure caused by pressure drop across the filter."

Based on information gleaned from US patent 6167746, it kind of looks like you need a balloon filled with warm (body temperature) air, and also some means for producing the requisite "hum" signal, I mean that's if you want to attack this thing in this way.  Also bear in mind that the device is recording in its memory everything you do to it, and it might be also taking pictures of you doing this.

Comments on Police State Madness:
An important observation to take away from all this, is that much of the "intelligence", in such a breathalyzer-ignition-interlock gizmo, takes place offline, and is done by humans.  That is to say there is this small army of human support staff, including installers, technicians, and analysts, if you can call them that, humans that go over the data logs, and look at pictures of you (and maybe other people and machines) starting your car.

Then there are people who know how to wag their finger, and make disapproving, tongue clicking,  "tch-tch" noises, in order to help you feel more ashamed.  You really can't underestimate the importance of that job, and I'm sure those people are paid well for what they do.

The reason it necessary to point out the existence of these people is to alleviate the misconception that automatic devices like this are living up the promise of automation. The device is not truly automatic, since it requires so many other people to make it work.  In fact it is really a labor-and-hassle creating device.

This is a point that tends to get overlooked by proponents of such devices. If you want to put one on every car, then there is necessarily a large scale surveillance industry needed to support all those devices, and this leads to a segment of the economy/society whose only job is spying on and shaming everyone else.  What percentage of GDP is a reasonable number to devote to bullshit like that anyway?  Who wants to live in a world where everyone getting paid to spy on everyone else?

Dear Jack A Lopez,

What a wonderfully expansive answer you have given.

You have answered all of the questions that were sloshing around in my brainbox.

I totally agree with you about folklore;
I spent a great deal of time researching the area of BBC TV detector vans  and the powers of the BBC detector staff because so much of what is  commonly believed did not make sense to me.

Virtually all of it was misinformation and folklore.

I particularly liked your findings on the humming/voice recognition part because I had doubts about that myself.

I only asked for an answer from someone in the industry because I find that a lot of Instructable answers are just guesses.

Thank you for your time, advice and solid answer.


Although this approach to drink driving seems ridiculous and impractical, the French are taking the first steps:


Mora and more the concept of being innocent until proven guilty is falling by the way side. The TSA assumes that everyone trying to get onto a plane is guilty of wanting to blow it up. So just buying a ticket makes you a suspect. This is where the real problem is, it is easier for law enforcement to "prevent" a crime from happening by believing that everyone is a criminal and thus needs to be monitored for that moment when they will act on their basic criminality, than it is for them to actually find and convict the true criminal who committed a crime without being observed. Using this philosophy they are dividing societies into 2 sectors, those who make laws and catch criminals and everyone else who is already determined to be a criminal because they are not in the first group. It is totally against to word and spirit of the US constitution but whether it will ever be declared as such is what will determine the future of civil rights.

This is a very good question, and I've wondered myself. I've never actually seen one in person.

If all it took was a blast of air, I would assume it could be easily defeated by blowing in some compressed air. I'm imagining some kind of device like a bulb you would squeeze.

I don't know if they are so sophisticated that they analyze the airflow so as to differentiate a real persons puff from that of a blast of air from some device.

I hope to never have any practical need to know, but it would be interesting to know.


6 years ago

Having all cars fitted with those would cause you major problems. The first and foremost being the cost. Then there would be the problem of regulating cars registered in other countries. Are all outside cars banned? Or do they all have to be stopped at the border and then fitted with the interlocks. And what about older cars?

Then there is the reality that stuff breaks. Adding a complex mechanism into a vehicle assures you that they will break more often and cause countless hours of grief for everyone.

It is legislation that presumes that everyone is a drunk driver.

A far better solution would be an enforcement system that keeps people from becoming repeat offenders. Something like loosing your license for 5 years and having your car confiscated for a first offense would be a much better deterrent.

It's stupid isn't it?
It can be electronically / electrically-hacked.


I knew someone who had the privilege of having one installed.
Its programed to the frequency of your voice, you have to hum into it to get it to start and his beeped every 10 minutes or so, so he couldn't be driving and drinking at the same time. The car wont shut off if you didn't blow into it while it ran, but it sent a report to whoever that he drove and didn't blow into it.

It's possible but I hope that they have more safeguards than that and are not so easy to defeat.

Um... It might, but I would hope that ANYONE in the area that saw someone using a balloon filled with "sober" air, trying to pass an in-car Breathalyzer machine would immediately call the police...