The invention relates to a field device for determining and/or monitoring a physical or chemical process parameter in automation technology, having at least one microcontroller (6), having a supply unit (2) having restricted capacity as the primary power supply and having a detection circuit (1) that signals a failure of the supply unit (2) to the microcontroller (6) by means of a detection signal early enough so that there is sufficient time to undertake appropriate security measures to prevent a loss of data, wherein the detection circuit (1) is designed such that a reference voltage required for the detection of a voltage drop in the supply unit (2) has a nearly constant offset to the supply voltage of the supply unit (2) and remains adapted to the supply voltage until the detection circuit (1) puts a detection signal through to the microcontroller (6) in the case of an erratic exceeding of the reference voltage or of an erratic voltage drop in the supply voltage.