The military have long been aware that RF emanations from electronic equipment can provide a great deal of information. The civilian world has generally paid little attention to this source of information. The technology for RF eavesdropping has become much less expensive so that now it is within reach of most anybody. This paper describes some low-cost technology that can be used for RF eavesdropping and explores how it can be used to obtain information from Beowulf clusters. It will also assess the prospects for developing this approach into a serious tool for compromising the security of Beowulf clusters.