A detector (10) for detecting an object (42) in a media item (40), such as a cheque or banknote is described. The detector (10) comprises first electrically conducting means (14), such as a roller, disposed on one side of a media path (32); second electrically conducting means (16), such as another roller, disposed on an opposing side of the media path (32); insulating means (30a,b) for electrically insulating the first and second conducting means (14,16); and impedance measuring means (38) for measuring the impedance between the first and second electrically conducting means (14,16). By measuring the impedance between the conducting means (14,16) it is possible to determine if an electrically conducting object (42) is being carried by a media item (40).