Localized magnetohydrodynamic modes occur frequently as precursors to dangerous plasma disruptions in tokamaks. Fast electron cyclotron emission (ECE) radiometry permits a space-resolved study of the dynamic behavior of these instabilities. Two types of multichannel, heterodyne ECE systems working on TEXTOR are briefly described. Temperature profile perturbations caused by tearing modes are shown. Typical Te fluctuations generated by rotating magnetic islands are presented. An early disruption warning system was built and tested on TEXTOR discharges. A real-time cross correlation calculation of two ECE signals is used to identify an m=2 mode. An analog alarm signal is generated then early during the instability evolution. An experimental test result is presented from a beam-heated tokamak plasma.