My brother is a state trooper in Mass. and the number and amount of “hides” he has found is staggering. It is not illegal to create a secret compartment in a car and there are body shops that specialize in this kind of construction.
One of the first finds he made was in an otherwise immaculate Mercedes where, after removing the driver and searching the car, he noticed a trace of blue wire from the running board. Mercedes is not that sloppy. So he got his kit and cut the wire and attached a battery and like magic a part of the back seat raised up uncovering a stash of drugs and money.
Like all good cops, he keeps a kit with various tools for detecting hides. Most amateur drug smugglers simply pull out the passenger side airbag and put the drugs or money or guns in there and replace the cover. Those are easy to find. Other smugglers put the radio on slides and use cash register solenoids and hook them up to the defrost button and brake pedal and the entire radio will slide out when the brake is depressed at the same time as the defrost button. There is absolutely no limit to the ingenuity of the smugglers.
Like all good cops my brother carries a drug detection kit that includes various tools, including a stethoscope and a reflex hammer. One time he stopped an 18 wheel flatbed trailer. He believed the driver was “dirty”, that is, moving drugs, but he couldn’t find any drugs in the truck and the driver was becoming snarky. He was going to cut the guy loose when he noticed the spare tire on the rack of the truck was brand new. With the stethoscope and hammer he tapped the tire and compared it to another spare. The tire made a noise as if something were in it and he called for a dog which hit on the tire — it had been filled with drugs and remounted on the rim. When the driver asked him how he knew he said, — “No trucker puts a new spare on the rack — they put the good tire on the truck and put the worn tire on the rack.” It was part of a new campaign by smugglers to mount tires on transcontinental trucks filled with drugs.
Some cars, such as the Toyota Camry, are known to have more dead space than others and therefore are more often used for drug smuggling. If you stand on the side of the road and stop thousands of cars you get to recognize the signs that a car is carrying drugs and if the courier is an amateur or a professional. For the most part, professionals get away. Dumb amateurs get caught. Those and the sloppy.