Finding Hidden Compartments

March 28, 2007
Since a hidden compartment will cool or heat differently than the surrounding surfaces, it can be visible on a thermal imager. This can make interdiction and investigations much easier.

Thank goodness for stupid criminals. I mean, really, thank goodness! Think of all the easy arrests and great stories you have developed over the years because of stupid criminals. Sometimes it's the bank robber who drives away in his car, which has personalized tags based on his name. Other times, it's the guy who leaves his motel room key on the convenience store counter after he takes $50 from the open register. Or, it can be the drug addict that tells you he has been clean for months, but when he stands, a crack pipe and a dime-bag of marijuana fall out of his lap. Stupid criminals are job security.

While the majority of criminals are not particularly bright, there are some that rise to the top. These crooks, if they put as much work into education as they do criminal activity, would probably be earning a third or fourth PhD degree. These smart criminals, while rare, are the ones that challenge us the most as police officers. These are the ones that make us stay on top of our game and constantly improve our skills and techniques. These are the ones, that when we bust them, we feel really proud.

Staying a step ahead

The smart criminals are also creative. They know that we, as law enforcement, have to play by certain rules when we try to catch them. They, of course, don't have any rules, so they are limited only by their imaginations. One area where we often see particular creativity is in the art of smuggling.

Smuggling in this context is not limited to movement across a border. For our purposes here, smuggling means secretly moving contraband from one place to another without detection. Smugglers have used everything from false-bottom suitcases, to swallowing their own contraband. Each method of concealment and carriage presents police officers with a host of detection challenges. Every time we figure out a way to reliably detect one method of smuggling, crooks have already evolved it to the next level, staying one step ahead of us in the race.

While they are not the exclusive method of movement, vehicles with hidden compartments are still a large conduit for the carriage and storage of contraband. Well-trained interdiction specialists may be able to find and dismantle a hidden compartment in just an hour or two. However, most of us do not receive that level of training. We may miss dozens of hidden compartments a year. That's where a thermal imager can help.

Using heat as a clue

Remember that a thermal imager only detects temperature differences. Different materials, especially when they have different densities, will absorb and release heat differently. Therefore, they will have different heat signatures. This can help you identify when one material has been used to hide a compartment, even though it appears to match the neighboring surfaces. For example, imagine a hole cut in the floorboard of a tractor with a sleeper cab. The entire floor is covered with carpet, making it appear the same visually. However, the metal flooring covered by carpet will heat and cool differently than the open hole covered by carpet alone. They have different densities, and the hole will cause a temperature difference to be visible on the TI.

This philosophy can be applied to any type of compartment in the truck, or any vehicle for that matter. Imagine 10 kilos of cocaine tucked behind the door panel. Normally, a door is relatively hollow, thus heating and cooling at a certain rate. The 10 kilos tucked in the door, however, will be denser than the hollow door. This will cause that particular area of the door to heat and cool at a different rate, making that area appear unique.

Odd void spaces can generate thermal signatures as well. These images show a hidden compartment made from the passenger airbag space. Because the airbag is missing, the dashboard heats and cools differently there. That temperature difference is visible on the thermal imager, indicated by the light gray rectangle. You can see in the still video image that the compartment is hinged.


While hidden compartments are not everyday occurrences, they probably occur more frequently than we realize. Because materials with different densities heat and cool at different rates, the presence of a hidden compartment may be visible with a thermal imager. This can give us one step up on those smart criminals, maybe even leading to one of those busts that make us so proud.

After all, anyone can arrest a stupid's catching those smart ones that is tough.

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