For the long-term clinical use of the wearable artificial endocrine pancreas, a fail-safe system is an essential mechanism. Several hardware alarm systems have been incorporated for battery-down, and short-run of the pumps. Software alarm systems for overflow or underflow of the AD converter, empty bags, hypoglycemia, hyperglycemia, abnormal values of parameters, and excessive insulin infusion have also been built into the system. The software noise filter was effective in eliminating superimposed artificial noises and the noises induced by muscle exercise. Sudden changes in sensor output during glycemic control of diabetics due to short circuit, or disconnection of the sensor lead, were detected as overflow or underflow of the AD converter. A gradual change in the sensor output was heralded by the hyper- or hypoglycemia alarm sound. These data indicated that the fail-safe system built into the wearable artificial endocrine pancreas is useful for the long-term glycemic control of diabetics.