Security marking
Last updated: September 4, 2008.
Hands off, it's mine! If you've spent a long time earning the
money to buy something nice—a flashy car, a shiny laptop, a whizzy
camera, or whatever it might be—the last thing you want is for
someone else to make off with it. But trying to stop people stealing
the things you own is never easy. Science is brilliant at solving
everyday problems like this, so how can it help us this time? Let's
look at some of the ingenious technologies people have developed for
stopping thieves in their tracks!
Photo: Mark your property with microscopic identification dots or
invisible ink and you'll stand a much better chance of getting it back.
Seeing the light?
The best intruder alarm in the world can't always keep thieves out
of your home and if your valuables get stolen they're often gone
for good. Even if the police catch the crooks and recover some of
their loot, how can they ever return it to its rightful owners? Who
knows which camera or TV belongs to which person? Science offers a
really easy solution! All you have to do is mark your property with
an invisible ink that shows up only in ultraviolet light. When
the police recover stolen property, they wave an ultraviolet lamp
over it, the markings (maybe your name or zip code) show up, and they
instantly find out to whom it belongs.
Photo: Ultraviolet lamps like this can be
used to show up the "invisible" security inks that deter thieves.
Photo by Warren Gretz courtesy of
US Department of Energy/National Renewable Energy Laboratory (DOE/NREL).
What is ultraviolet light?
Our eyes can see only a limited range of all the electromagnetic
energy that zaps through the world—things like radio waves,
microwaves, X-rays, and so on. We call the energy we can see visible
light and, like radio waves,
microwaves (the ones that cook food in microwave ovens), and all the rest, it's made
up of electromagnetic waves that race along at the speed of light
(300,000 km per second or 186,000 miles per second, which is fast enough to
go 400 times round the world in a minute!). The light we
can see stretches in a spectrum from red (the lowest frequency and
longest wavelength of light our eyes can register) through orange, yellow,
green, blue, and indigo to violet (the highest frequency and shortest
wavelength we can see). Just beyond the reddest light we can see, with a
slightly shorter frequency, there's a kind of invisible light called
infrared. Although we can't see it, we can feel it warming our skin
when it hits our face—it's what we think of as radiated heat. In the
same way, there's a kind of blue-ish light just beyond the
highest-frequency violet light that our eyes can detect. That's
called ultraviolet. It's present in sunlight and too much of it burns your
skin (that's why you need sunscreen).
Now, if the ink is invisible and shows up only in invisible
ultraviolet light, how come you can see it when you shine one of
those special lights on it? If you've read our article on light,
you'll know that atoms make light when they absorb energy, become
unstable, and then emit (give out) the same energy a few moments
later. What happens with security ink is that the atoms absorb
ultraviolet light, become unstable, but then give out a slightly
different, blueish light that our eyes can see. (This is like the
process that happens in the white outer coating of a
fluorescent lamp, which converts ultraviolet light made inside the tube into
visible light that brightens up our homes.)
Dodgy dots?
Of course, really savvy thieves could simply go out and buy an
ultraviolet light, wave it over the things they steal, find the
security markings and obliterate them. Is there anything science can
do about that? An Australian company called DataDot Technology has
come up with one possible solution. Instead of marking your property
with invisible ink, you spray it with thousands of invisible
"microdots" that store details of who your are. The dots are tiny
glue particles onto which a special identification number is etched
with a laser (and the details of who each number belongs to are
recorded on a computer database).
Each dot is about as big
as a grain of sand and has to be magnified at least 50 times before
it shows up. It's easy to cover every part of a car and its engine
with these magical markers, but it doesn't matter if thieves know
they're there; sometimes it even helps! One crime study in Australia
found that DataDots reduced car theft by over 60 percent; once thieves
know something is marked, they know it'll be harder to sell on and
they take their dodgy business elsewhere.
Help, I'm being stolen!
Opportunistic theft is a really big problem in stores, but
technology can help to solve that problem too. As many retailers have
discovered, all you have to do is fit a tiny RFID radio tag onto the
merchandise you're selling and put a couple of detector gates in the
doorway. If someone tries to steal something, the radio tag triggers
an alarm as it passes through the gates. You can read more about this
in our main article on RFID.
Photo: An RFID gate in a shop doorway. It works in two ways at once: you know the alarm will go off if you try to steal something so you think twice—it's a deterrent as well as an alarm.
