A microcontroller system includes a microcontroller, a device which is controllable by the microcontroller, and a monitoring device. Under the control of a normal operation program, the microcontroller outputs a normal operation indicating signal. If the normal operation indicating signal is absent, the monitoring device transfers the device into a secured state and, if it is absent over a predefined period of time, locks the device in that state. When predefined exceptional conditions occur, the microcontroller changes to an operation preparation program, and the monitoring device increments a register. If the contents of the register reach a predefined value, the monitoring device locks the device in the secured state.