I don't know, but we have several signs and yet I have still needed to ask patients to stop. It probably happens once or twice a month. Not quite as frequent is those who try to video their procedure. While I get irritated, I'd get more bothered by not being able to make or receive calls myself if a jammer was installed. A good compromise is to have patients seated near an MRI Faraday cage - it works just as well and doesn't break laws.