Abstract: A microprocessor based device which monitors the operation of a compressor in a refrigeration system and automatically shuts the compressor down if a monitored condition is abnormal. Sensors in the refrigeration system sense conditions such as refrigerant pressure and temperature, superheat, oil pressure and motor current draw. If a sensed condition is outside of a safety range and remains there for a time out period, an alarm condition is indicated and the device generates a alarm signal and shuts down the compressor. A detachable display module includes a keypad for carrying out field programming and a LCD screen for displaying the refrigerant conditions and programming prompts and commands. A rest button permits resetting twice before a service call is required.