Microprocessor-controlled temperature controller with temperature reduction at night, visual alarm and inverting function for heating/cooling. The temperature controller is equipped with an LED lamp to indicate the activity of connected heating or cooling devices. When switching into programming mode, the slot for external devices is deactivated for safety reasons. To protect the electronic components, a delay of 60 seconds is set between two switching states before the slot becomes active again. Break or a short-circuit are indicated as faults. The temperature sensor is equipped with a USB connector for replacement in the event of a defect.