# Legal / Engineering Question: Device for Jamming Nearby Cellphones **URL:** \ **Category:** Factual Questions\ **Created:** [May 12, 2001, 1:57pm UTC](https://boards.straightdope.com/t/legal-engineering-question-device-for-jamming-nearby-cellphones/65212 "2001-05-12T13:57:09Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Autumn\_Wind\_Chick](https://avatars.discourse-cdn.com/v4/letter/a/6a8cbe/32.png) [@Autumn\_Wind\_Chick](https://boards.straightdope.com/u/Autumn_Wind_Chick)\ **Post date:** [May 12, 2001, 1:57pm UTC](https://boards.straightdope.com/t/legal-engineering-question-device-for-jamming-nearby-cellphones/65212/1 "2001-05-12T13:57:09Z")
Would it be difficult to make such a device? Would it fit in the trunk of my car? My purse? Is it legal? What would the penalties be if I got caught? ---
**Author:** ![Chas.E](https://avatars.discourse-cdn.com/v4/letter/c/e99b99/32.png) [@Chas.E](https://boards.straightdope.com/u/Chas.E)\ **Post date:** [May 12, 2001, 2:28pm UTC](https://boards.straightdope.com/t/legal-engineering-question-device-for-jamming-nearby-cellphones/65212/2 "2001-05-12T14:28:24Z")
It is illegal to broadcast any radio interference that disrupts radio communications. The only legal way to disrupt cellular phones is with shielding. You could build a Faraday Cage, which stops all radio signals from penetrating. Not a very practical method, but it would work for a building interior. All you have to do is make a room that is completely lined with a fine mesh of copper screen. The door would be a little tricky, you’d have to make a “trap” but that is not an insurmountable obstacle. But overall, blocking cellular phones is a stupid idea. Do you really want to have your doctor sitting in a restaurant with a cellular blocker, when you have a heart attack and he’s on call? ---
**Author:** ![waterj2](https://avatars.discourse-cdn.com/v4/letter/w/858c86/32.png) [@waterj2](https://boards.straightdope.com/u/waterj2)\ **Post date:** [May 12, 2001, 2:33pm UTC](https://boards.straightdope.com/t/legal-engineering-question-device-for-jamming-nearby-cellphones/65212/3 "2001-05-12T14:33:00Z")
I believe that it’s illegal to jam cell phone signals. The FCC doesn’t take too high a view of people interfering with sections of the electromagnetic spectrum that it has sold to others. Basically, the cell phone companies own those frequencies outright, and jamming them is going to be looked on as badly as tresspassing on their property to interfere with them doing business. If caught, expect to be prosecuted to the full extent of the law, whatever that is. Of course, I could be wrong. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [May 12, 2001, 3:13pm UTC](https://boards.straightdope.com/t/legal-engineering-question-device-for-jamming-nearby-cellphones/65212/4 "2001-05-12T15:13:23Z")
"Would it be difficult to make such a device? " I think the main trouble you’d have would be finding a schematic for one. It’s not the sort of information that the government/corporations want everyone to have access to. There was an Israeli company that made the things a couple years back, but a quick Google search doesn’t turn up much current info on availability. “Would it fit in the trunk of my car? My purse?” It shouldn’t need much power, so yes, one would probably fit in a purse. “Is it legal?” Probably not for private individuals. ---
**Author:** ![ModernRonin2](https://avatars.discourse-cdn.com/v4/letter/m/c37758/32.png) [@ModernRonin2](https://boards.straightdope.com/u/ModernRonin2)\ **Post date:** [May 12, 2001, 9:38pm UTC](https://boards.straightdope.com/t/legal-engineering-question-device-for-jamming-nearby-cellphones/65212/5 "2001-05-12T21:38:38Z")
\Would it be difficult to make such a device? \ Define “difficult”. A college-level electrical engineer could easily assemeble one, given the parts. Coming up with one from scratch is much harder. You’d have to be a professional RF engineer. But it can be, and has been, done. \Would it fit in the trunk of my car? My purse? \ The trunk of your car would be way more than enough space, though you’d have to be careful since metal blocks radio signals. Inside the trunk is surrounded by metal body panels, which would choke the signal dramatically. Your purse… yesh, probably. The problem there is not so much the radio-transmitter circuitry, it’s the batteries required to power it. RF transmission is a very power-hungry process, which is why even a half-pound jumbo cell phone battery only lasts about an hour of “on-air” talking time. (Though a lot longer on standby when the phone doesn’t need to actually broadcast radio waves.) Since cell phones operate in the microwave band, you may want to consider carefully putting a powerful microwave transmitter down near your reproductive organs. ;] \Is it legal?\ In general, no. Any radio transmission (except on a few “free” bands) that broadcasts at a power greater than 1 milli-watt requires an FCC license. In addition, intentionally causiong radio interference is technically illegal. A 1mW transmission power cell-phone jammer would protect only a very small area around it. Exactly how much is influenced by several factors - how strong the cell phone signals are at that place, how good the receiver circuitry inside the cell phone you’re trying to jam is, etc, etc… In the absolute best case, with a really good antenna, set in the perfect location, and a really smart and sophisticated jammer you might get a 15-foot radius out of a 1mW jammer. You can of course make a jammer that transmits stronger. But it’ll munch through batteries and will be blatantly illegal, instead of only slightly illegal. \What would the penalties be if I got caught? \ I believe the maximum penalty the FCC can impose for signal jamming is $100,000 and a year in prison. Or something along those lines. URLs follow… [http://www.msnbc.com/news/544178.asp?cp1=1](http://www.msnbc.com/news/544178.asp?cp1=1) - An MS-NBC story about cell-phone jammers. [http://www.cguard.com](http://www.cguard.com) - This is a company in Isreal that sells “cellular firewalls”, aka cell phone jammers. They sell 500mw as well as 30W (30,000mW!!!) jammers. [http://starportuk.com/21.htm](http://starportuk.com/21.htm) - A UK company with less powerful cell phone jammers. (150 mW, good enough for a conference room or hotel room.) Order on-line with a credit card - they claim shipping is next business day! -Ben