Hendrik Witt examines user interfaces for wearable computers and analyses the challenges imposed by the wearable computing paradigm through its dual-task character. He introduces a special software tool as well as the "HotWire" evaluation method to facilitate user interface development and evaluation. Based on the results of different end-user experiments conducted to study the management of interruptions with gesture and speech input in a wearable computing scenario, the author derives design guidelines and general constraints for forthcoming interface designs.