How Stuff Works: Cell Phone Jammers

Cell phones are a large part of society today, and almost every has them. Sometimes they’re used inappropriately, like in quite places like restaurants, or you’ll find someone who feels the need to talk extra loud. Wouldn’t it be nice to jam their signal? There are such devices on the market, but in most countries it’s highly illegal for a civilian to use one. I was reading the HowStuffWorks page on jamming cell phones, and found it very interesting. Some companies are trying to legalize the equipment for law enforcement officers in the name of terror. This meaning they would be able to thwart a terror attack that involves remotely detonating bombs with cell phones. They also claim it would help in drug busts. After hearing about the controversy about legalizing these devices for certain people, I became interested in how they work.

Basically jamming is done the same way you can remotely deny service to a computer. The jammer sends a signal that is the same frequency of the cell phone, which interrupts the signal it gets from the tower. They even have the same name “denial of service act”. The signal the jammer transmits is stronger than the cell phone tower they are near, so the cell phone uses that “tower” instead of the real one.

Cell phones like some nic cards are full duplex. They have the ability to simultaneously upload and download data. Some jammers jam only upload, while others jam download. Good jammers will jam both upload and download. Home brew jammers can jam distances of up to 30 feet, while ones professionally made can jam about 100 yards. If you’re using an industrial strength jammer for law enforcement (not in the U.S) you can jam up to a whole mile.

If you do manage to get your hands on a home brew one, watch out the fines are hefty. For a first offence it’s as much as an $11,000 fine, or one year in prison.