Device Detects Drug Use Through Fingerprints, Raising A Host Of Constitutional Questions

from the defendant-has-indicated-gov't-will-receive-'two-fingers-while-he's-s dept

If this tech becomes a routine part of law enforcement loadouts, judicial Fourth and Fifth Amendment findings are going to be upended. Or, at least, they should be. I guess citizens will just have to see how this all shakes out.

A raft of sensitive new fingerprint-analysis techniques is proving to be a potentially powerful, and in some cases worrying, new avenue for extracting intimate personal information—including what drugs a person has used.


The new methods use biometrics to analyze biochemical traces in sweat found along the ridges of a fingerprint. And those trace chemicals can quickly reveal whether you have ingested cocaine, opiates, marijuana, or other drugs. One novel, noninvasive forensic technique developed by researchers at the University of Surrey in the United Kingdom can detect cocaine and opiate use from a fingerprint in as little as 30 seconds. The team collected 160 fingerprint samples from 16 individuals at a drug-treatment center who had used cocaine within the past 24 hours—confirmed by saliva testing—along with 80 samples from non-users. The assay—which was so sensitive that it could still detect trace amounts of cocaine after subjects washed their hands with soap—correctly identified 99 percent of the users, and gave false positive results for just 2.5 percent of the nonusers, according to a paper published in Clinical Chemistry.

Let’s discuss the phrase “non-invasive.” It was relatively non-invasive when fingerprints were simply used to identify people. (That science isn’t exactly settled, but we’ll set that aside for now.) When smartphones and other devices used fingerprint scanners for ID, the “non-invasive” application of fingerprints was no longer non-invasive. An identifying mark, possessing no Fifth Amendment protection, gave law enforcement and prosecutors the option of using something deemed “non-testimonial” to obtain plenty of evidence to be used against the fingerprinted.

This opens up a whole new Constitutional Pandora’s Box by giving officers the potential to apply fingerprints during traffic stops to see if they can’t generate enough probable cause to perform a warrantless search of the car and everyone in it. It’s generally criminal to possess drugs. Evidence of ingested drugs means suspects possessed them at some point in time, but evidence of drug use is generally only useful in driving under the influence cases. That’s in terms of prosecutions, though. For roadside searches — where officers so very frequently “smell marijuana” — evidence of drug use is a free pass for warrantless searches.

That’s just the Fourth Amendment side. The Fifth Amendment side is its own animal. Evidence obtained through fingerprints would seemingly make the production of fingerprints subject to Fifth Amendment protections. It should at least rise to the level of blood draws and breath tests, even though this is far more intrusive (in terms of evidence obtained) than tech normally deployed at DUI checkpoints. Blood draws often require warrants. Breath tests, depending on surrounding circumstances, aren’t nearly as settled, with courts often finding obtaining carbon dioxide from breathing humans to be minimally testimonial.

As Scott Greenfield points out, the first tests of constitutionality will occur at street level. Cops will deploy the tech, hoping to good faith their way past constitutional challenges.

Precedent holds that the police are authorized to seize people’s fingerprints upon arrest, as the Fifth Amendment does not apply to physical characteristics. But the rubric is “fingerprints can be seized” based on their limited utility as physical characteristics used for identification purposes.

If they should be used for entirely different purposes, for the ascertainment of whether a person ingested drugs, then the rationale allowing the seizure of prints under the Fifth Amendment no longer applies. It certainly won’t be in the cops’ best interests to draw this distinction, to limit their use of prints to the purpose for which they’re allowed and to demonstrate constitutional restraint by not exceeding that purpose.

This means everything will get much worse for drivers and other recipients of law enforcement attention in the short-term. When the challenges to searches and seizures filter their way up through the court system, things might improve. But it won’t happen rapidly and any judges leaning towards redefining the scope of fingerprint use will face strong government challenges.

It will probably be argued evidence of drug use obtained through these devices is no different than a cop catching a whiff of marijuana. On one hand, no cop could credibly claim to be able to detect drug use simply by touching someone’s fingers. On the other hand, the reasonable reliability of the tech makes challenges more difficult than arguing against an officer’s claim they smelled drugs during the traffic stop. The key may be predicating a challenge on the fact that the device actually tests sweat, not fingerprints, making it an issue of bodily fluids again and (slightly) raising the bar for law enforcement.

This news isn’t disturbing for what it is. The obvious initial application is in workplaces, where random drug tests are standard policies for many companies. That tech advancements would progress to this point — a 10-minute test that requires only the momentary placement of a finger on a test strip — was inevitable. It’s what comes after that will be significant. Courts have often cut law enforcement a lot of slack and tend to lag far behind tech developments and their implications on Constitutional rights. A new way to obtain evidence using something courts generally don’t consider to be testimonial is going to disrupt the Constitution. Hopefully, the courts will recognize the distinction between identification and evidence and rule appropriately.

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Comments on “Device Detects Drug Use Through Fingerprints, Raising A Host Of Constitutional Questions”

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Anonymous Coward says:

Yes, let’s talk about the term non-invasive. A term used, as far as I can tell, solely by Dr Bailey (PhD in Electrical Engineering, in case you were wondering) in the context of a new medical diagnostic technique. In the field (and by this I mean literally every scientific field from medicine to biology to god-damn physics), non-invasive refers to any technique which does not require insertion of an instrument into the sample space.

In medicine (where it is by far most commonly used) this would refer to any diagnostic test, surgery, or other treatment which does not require insertion of an instrument inside the patient’s body. Every single piece of context in your linked sources clearly shows that she was discussing their new medical diagnostic technique, which is clearly non-invasive. Period. End of story.

Either you didn’t know this, in which case the lack of even a basic attempt at background research is, frankly, appalling. Or you did, in which case blatantly taking quotes completely out of context might actually be worse.

Either way, there are some serious journalistic ethics issues here.

Anonymous Coward says:

Re: Invasion of privacy, not invasion of object

It’s pretty clear from context that this is about whether the technique invades a realm protected by Constitutional rights, not about whether it can be done without invading a physical body. It’s “non-invasive” to collect information that historically has not, and reasonably should not, require judicial approval, such as photographing a detainee. It’s “invasive” to collect information that reasonably should require judicial approval, often because it is testimonial and can be used to incriminate the person.

Roger Strong (profile) says:

Re: Re:

Word games.

A more relevant case would be police use of thermal imaging cameras to scan peoples’ homes for grow-op lamps.

The Supreme Court ruled that no, they can’t do that.

It did so, the court said, because the device is not in general use by the public, so Kyllo had an expectation of privacy, and because the imaging provided by the camera revealed details about Kyllo’s home "that would previously have been unknowable without physical intrusion."


Kyllo’s attorney, Kenneth Lerner, made a similar argument in court papers: "Technology that exploits invisible, sub-sensory phenomena ultimately fails to respect the traditional boundaries of society, and therefore leaves the population defenseless against such surveillance."

Even if we accept your surgery definition of "invasive" – as opposed to an invasion of privacy – the court would appear to disagree with you.

But the court said the Fourth Amendment was applicable since the search provided information regarding the home’s interior that otherwise could not have been obtained without a physical intrusion.

HegemonicDistortion says:

Re: Re:

Reading comprehension fail. The points in this piece as they pertain to the word "noninvasive" aren’t at all about the medical meaning. Quite the opposite, it’s entirely predicated on that correct meaning. Here, it’s just a rhetorical reuse of the word in terms of its implications in law and civil liberties, contrasting the very different implications of that noninvasiveness in medical vs legal contexts — to wit, the ability for officers to "search" an individual for evidence of criminal behavior (from something every person leaves behind every minute of their lives) without any prior suspicion. It’s the noninvasive nature (medical) of the diagnostic technique that creates the great potential for invasive (legal) abuse by officers.

Ethically, it’s obvious you’re attempting to discredit very important discussion of civil liberty concerns by denigrating the piece and the author via a bogus use of pedantic "concerns" that are entirely deceptive as to the point of the piece.

DannyB (profile) says:

Re: Re:

let’s talk about the term non-invasive.

I would rather talk about the term false positive.

2.5% may not sound like much. Unless your test result happens to fall into the false positives and your life and career are destroyed by overzealous cops who were kind enough not to just shoot you on the spot — uh, because of um, something.

We’re talking about an extremely sensitive test here. What if you test positive because your fingerprint ridges have some illicit drug that you happened to pick up by merely handling currency.

Oh, wait. Only criminals use actual cash which is anonymous. Law abiding citizens have no need to be anonymous and would know that all good people do not use cash so that their entire life is open to inspection to the government. For their own good.

Anonymous Coward says:

Re: Re: Re:

2.5% is a horrible false positive rate (unless you’re a cop). Out of a company of 1000, you are talking about 25 being taken to task for improper reasons. And that is per iteration of testing.

Monthly testing? Good luck keeping folks on after the first year of drug-testing RIFs.

Of course, that’s just the innocent…

btr1701 (profile) says:

Re: Re: Re:

I would rather talk about the term false positive. 2.5%
> may not sound like much. Unless your test result happens
> to fall into the false positives and your life and career
> are destroyed

And can this test distinguish between drug residue on the fingers because of the person’s drug use and drug residue on the fingers because the person happened to touch something (a doorknob, a steering wheel, a restaurant chair) that had drug residue on it?

MathFox says:


A poppy-seed bagel will likely (make you) test positive on opiates. The yeast used for making the dough rise produces alcohol (evaporates in the baking process). Add some coke from the dollar bills you get back as change…

I would not suggest to use a fingerprint test like this for conviction; use a proper blood analysis instead.

Uriel-238 (profile) says:

Re: Are these tests verified outside of law enforcement?

Given we’ve established the police are eager for tests that provide false positives and are accepted in court as evidence of crime (and justification to put warm bodies into prison) has anyone not allied with law enforcement submitted reports as to the accuracy and veracity of these tests?

Narcissus (profile) says:

Drug use != criminal?

Why is there so much focus on catching drug users and not drug traffickers? Methinks the drug users are victims more than criminals.

If somebody has 3 pounds of cocaine in the trunk of his car please arrest him. If somebody has used drugs and has a small amount on him. Give him a stern warning and a flyer for a rehab center.

teka says:

Re: Drug use != criminal?

But someone with pounds of drugs stacked like bricks in their car might be a challenging, violent individual with friends while picking up Kevin, who smoked a joint with some friends at that concert over the weekend, is entirely nonviolent, peaceful and even meek in the face of military-style troop carriers and weapons being swung around by khaki clad not-soldiers. They get to win And to be entirely selective and risk averse.

Daydream says:

2.5% is a pretty big error rate.

I googled; the percentage of Americans who use drugs is estimated to be as high as 1 in 10. 2.5% is 1 in 40.

So like, if you have a group of 50 people in a room, yeah, maybe 5 of them will turn out to be drug users. But there’s a good chance you’ll pick up a 6th who hasn’t so much as used an asthma inhaler.

And that 2.5% was testing under controlled conditions; what happens in the real world where people have touched all sorts of things?

Anonymous Coward says:

Re: Re: 2.5% is a pretty big error rate.

Fingers and hands are by far the most contaminated parts of a person’s body. Even if the Western European custom of hand-shaking were to be successfully outlawed, there are still far too many sources of potential contamination that would render any such drug-test-via-fingerprint system basically useless.

Anonymous Coward says:

Re: 2.5% is a pretty big error rate.

Actually, you are understating the accuracy problem. As of 2013 (the most recent year that I have numbers for), the percentages of the population using the most popular illicit drugs are as follows: pot – 6.2%, prescription drugs without a prescription – 2.1%, cocaine – 0.5%, hallucinogens – 0.4%, meth – 0.2%, heroin – 0.1%. Which means that the true positive rate, the percentage of people with a positive test who are actually on the drug indicated, would be (by Bayes’ Law): pot – 72%, prescription drugs – 46%, cocaine – 17%, hallucinogens – 14%, meth – 7%, heroin – 4%. Though I wouldn’t doubt that test results would be advertised as 99% accurate (prosecutor’s fallacy and all).

Bruce C. says:

Another can of worms...

Will there be a differentiation between latent fingerprints left at a crime scene vs. prints taken off of you onsite? If the tech can pull the analysis off of fingerprints hours or days after you’ve left them, they’d probably be admissable under the same standards as other crime-scene evidence such as DNA.

Is there an expectation of privacy if you leave a fingerprint in a public place rather than in a private home? Could a cop go undercover at a restaurant favored by a suspect to gather fingerprints for chemical analysis?

Anonymous Coward says:

We the Sheeple……….
Who have blindly given away our Rights ………
In the facially of Security ………………..
Now Question our Masters Overreach ? ……………..
Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha Ha…………………………………………………………………………………………………………….

Anonymous Coward says:

Actually, raising worries only for drug users.

Regular readers will recognize Techdirt’s ongoing concern that drug users, prostitutes, and child pornographers might NOT escape through some legalistic technicality.

This is EXTERNAL examination, so completely without the obstacles that Techdirt hopes for.

Anonymous Coward says:

Fingerprints during traffic stops

This opens up a whole new Constitutional Pandora’s Box by giving officers the potential to apply fingerprints during traffic stops to see if they can’t generate enough probable cause to perform a warrantless search of the car and everyone in it.

Citation needed. Has a court found that police can compel fingerprints during traffic stops? They can certainly do it after upon arrest, but they can’t arrest without probable cause, and refusing to provide a fingerprint wouldn’t be probable cause (unless some law makes that a crime in and of itself, as with breath samples).

Anonymous Coward says:

Re: Fingerprints during traffic stops

But you are forced to sign the traffic ticket, or else you will be arrested and taken to jail. In doing so, you are also by default leaving your fingerprints.

Although many retail establishments require the collection of fingerprints when conducting certain financial transactons, for some reason police don’t – yet – when signing for a traffic ticket.

Maybe that will soon change. The border police have for decades collected fingerprints from people they stop, and this is their primary method of instant identification, since illegal aliens typically don’t carry any sort of identity cards for obvious reasons.

ECA (profile) says:


Its a wonder that it take a Major test to indicate MJ in the blood stream..
One that CANT BE administered onsite..

You are telling me that they CAN/will soon have a device that can Check for MOST drugs, from the oil Secreted from our skin?

AT any level..Like a breathalyzer..for the skin.
1. it has to have an oil base..(dont eat the cookies)
2. Cause you tested for something, does NOT MEAN it was recent.. And that a friend NEAR them, DID IT…not them..
3. instant test?? not in MOST formats, unless you can test INSIDE THE MOUTH, or blood test..

IF they aint going to FIX the problem, WHy put people in jail..
The Rule says that IF you did not create a traffic infraction, THEY CANT STOP YOU…Test you or anything else..

How many false positives BEFORE they give it up??

bshock says:

I’m primarily interested in the probability of false positives during these tests. In the past, a huge amount of test equipment given to police officers has come with a ridiculous rate of false positives, to the point where carrying loose-leaf green tea would almost certainly get you hauled in for marijuana possession. (Not that the persisting illegality of marijuana makes any sense, either.)

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