In ths U.S., at least, it is illegal to block/interfere with cellular transmissions -- even for prisons (there are employees and visitors with cell phones, near

In ths U.S., at least, it is illegal to block/interfere with cellular transmissions -- even for prisons (there are employees and visitors with cell phones, nearby homes, etc.). I recall reading an article about how one prison in particular was using DF equipment to track down phones since they couldn't block them.