Went on an exchange trip to Beijing and these things are encouraged and legal in China to stop cheating and SMS in class. They are brilliant. Severly tempted to buy one. Don't be put off by the mumbo jumbo of 'it can mak pacemakers stop and aircraft crash' rubbish. Thousands of people use mobile phones at airports and hospitals and I have never heard of any problems. The small personal jammers have a range of 5-10 metres, enough for a classroom. The size of an MP4 player or small mobile phone, I am getting one to use at school and stuff the law!