Is there any way to detect high tech (e.g. cell-phone assisted) academic dishonesty? Over the last few years, our university has seen a rise in high-tech academic dishonesty.  We have a no electronics policy, except calculators when needed (even those now are provided by the school, and personal calculators are not allowed).  However, students still sneak cell phones into the exam and use them in a very inconspicuous way.  

We have had students take pictures (presumably with a cell phone) during an exam and have someone outside the room sending them back solutions. We have had them communicate with classmates somewhere else in the room (some have been caught this way giving the right answers to the wrong exam).  We have had numerous students using their phones to store notes, copies of old exam solutions, etc., and use them as an aid during the exam (this is the most common). 

We have caught some students, but I know it is a small fraction. Students will tell us they see cell phone use routinely during exams, but don't want to squeal on classmates because of anticipated reprisal.  Our instructors are quite vigilant in watching the classroom, but it is very difficult to watch 30 to 70 students constantly.  (Larger classes have multiple proctors.)  Instructors have been informed of the classic cues as well.  Our penalties are stiff (first offense, F in the course, second offense, student gets the boot from the school). However, students are still getting away with high-tech cheating.  

My question is, does anyone have any sure fire ways of identifying students attempting to use cell phones or other high-tech cheating devices during exams? I'm looking for methods, electronic sniffers, etc.
Ultimately, this is not a technological problem but a cultural and pedagogical problem.

The problem with technological solutions is that they set up an "arms race" with the students, in which you will certainly lose.  Electronics are constantly getting smaller and obtaining more means of communication, so a student who really wants to cheat will likely have a means that you won't be readily able to distinguish.  Consider, for example, the recent emergence of smart watches: are you going to ban watches from the classroom?  What about low-tech but still effective forms of cheating like scraps of paper?  If you get a frequency scanner, will you be able to catch somebody using non-standard communication bands?

The best defense against cheating students is other students who understand that it cheats them out of the value of their well-earned grades.  If you can inculcate a school culture where most students are not just not cheating but actively opposed to cheating, then it will be much harder for cheaters to prosper.

The second best defense against cheating is to design exams that are more about process than product.  Think "show your work" and "essay question."  Yes, it's possible that a cheating student will outsource their work and render themselves a puppet of an expert whispering guidance in their ear, but that's a lot harder to do than secretly googling for information about Kirchoff's laws.  I am, in fact, a big fan of open-book tests, which tend to push students to focus on synthesis instead of memorization. This, I believe, has much more value to students in the long run, and also has the nice side effect of rendering high-tech cheating much less valuable as well.