The Wall Street Journal has been reporting about how students have taken to cheating on exams with cell phones, mainly by using camera phones to create tiny digital cheat sheets (WSJ subscription required for these links.) Five "e-cheaters" in China are facing criminal charges of stealing state secrets for text messaging answers to a college entrance exam. While some school districts (including New York City) ban cell phones entirely, it's unlikely that the move will be widespread because parents want the ability to reach their children in case of emergencies. Now, instead, some schools are fighting back with devices to find cell phones and sometimes render them useless.
Cell Busters Cell Phone Detector will detect the presence of cell signals in the air and flash a 'red alert' as well as an audio warning to turn off the phone. SafeHaven disables the camera function in phones when a signal is detected. The apparently unironically named company Cell Block makes something called Quiet Cell which not only detects the cell signal but disables calling. The FCC doesn't allow blocking of licensed telecommunications, so Cell Block won't get far in the U.S., at least for now.