[en] Segmented Au-Ni nanowires are demonstrated to be highly effective thermocouples with a spatial resolution of a few nanometers and a temporal resolution in the microsecond range. The performance of the devices is characterized by a self-heating procedure in which an ac heating current with frequency ω is applied on the wires while monitoring the resulting thermoelectric voltage V_TH at 2ω using a lock-in technique. An analytical model is developed that enables one to determine the time response of the thermocouples from plots of V_TH as a function of ω