This paper describes results on Built-In Current Sensors destined to overcome the limitations of IDDQ testing in deep submicron circuits. The problems of performance penalty, test accuracy and test speed are addressed. A new sensor composed of a source-controlled comparator operating at low supply voltages and bias currents is used. Gradual sensor activation ensures reliable low noise operation. It is combined with large bypass MOS switches avoiding performance penalty, as well as a second bypass and compensation logic to increase test speed.