Abstract: The supply of cryogenic fluid used for controlled storage environment of biological materials is monitored so as to insure an adequate level. The monitoring is effected by employing a beam balance mechanism. Counterweights associated with the beam balance are adjusted for providing a balance arm transition around a horizontal axis when the total weight of the container including the biological materials and the cryogenic refrigerant has dropped below a predetermined threshold. A sensing switch associated with the arm of the beam balance actuates an alarm circuit when the weight threshold has been passed.