Who cares? A jammer that can easily be hidden cost 50$. Buy 4 of them and place one in every corner of the restaurant above the ceiling and now there is no longer cell phone reception (Or internet). You can't stop things like this, get over it.
But, it's illegal and the jammers can easily be detected. Then you'll be driven out of business by the government. The cathedral in Mexico City gets all of the elite funerals. Elite funerals attract reporters. Reporters in Mexico City noticed that their cell phones didn't work in the cathedral but they had before. They quickly discovered the cell service was being blocked during church services. But, in Mexico, it isn't illegal so I assume they're still being blocked.
So they can stop an employee having a jammer in their pocket that looks like a cigarette pack? You guys really don't understand how this works. You honestly can't stop it.
It would be easy to build a building in which cell phone signals were blocked, legally. Just make it a Faraday cage (basically a grounded metal cage). I know I barely get signal in my local Wal-Mart, which is basically a metal warehouse. - - - Updated - - - Cell phone jammers put out radio signals. The FCC can find them very easily if they want (for example, complaints). Of course it can be stopped. That, or one disgruntled employee....... The penalties are up to $112,500 per act. http://fjallfoss.fcc.gov/edocs_public/attachmatch/DA-12-1642A1.pdf
