Complex sentence: In the 1980s, Soviet evesdroppers were known to plant bugs inside IBM Selectric typewriters to monitor the electrical noise generated as the type ball rotated and pitched to strike the paper; the characteristics of those signals could determine which key was pressed.
Split into simpler sentences: In the 1980s, Soviet evesdroppers were known to plant bugs inside IBM Selectric typewriters to monitor the electrical noise generated as the type ball rotated and pitched to strike the paper. The characteristics of those signals could determine which key was pressed.