The invention relates to a device (1) and a method for measuring the moisture in die cast molds (24), the cavity (25) of which is connected via an evacuation conduit (31) to an evacuation device (28). The modular assembly of the device (1) is connectable to the evacuation conduit (31) and comprises a sensor assembly (S) by means of which the moisture of gases evacuated from the mold cavity (25) is measurable. The sensor assembly (S) comprises an emitter (7) emitting electromagnetic radiation and a detector (14) detecting electromagnetic radiation. On the basis of the measured values obtained during the evacuation action it can be determined whether the amount of a water/release agent mixture jetted into the mold cavity (25) needs to be altered before the actual casting action.