A method of detecting a loss of a refrigerant from a refrigerant circuit comprising at least one condenser, at least one compressor, and at least one evaporator having an outlet port, and at least one expansion valve having an inlet port and an outlet port, the refrigerant circuit also comprising a first sensor for recording a thermodynamic state of the refrigerant at the inlet port of the at least one expansion valve and/or a thermodynamic state of the refrigerant at or near the at least one condenser, and a second sensor for recording a thermodynamic state of the refrigerant at the outlet port of the at least one evaporator, the method comprising the steps of: recording a first signal indicative of a thermodynamic state of the refrigerant using the first sensor; recording a second signal indicative of a thermodynamic state of the refrigerant using the second sensor; characterised in that the method comprises the steps of determining a first value of maximum available capacity of the refrigerant circuit as a function of the first and second signals; recording a third signal, the third signal being - a signal indicative of power currently dissipated by the at least one evaporator; determining a first value of current capacity of the refrigerant circuit as a function of the third signal; determining a first ratio by relating the first value of current capacity to the first value of maximum available capacity; and if the determined first ratio exceeds one by a first threshold: producing a first alarm signal indicative of the loss of the refrigerant; further characterised in that the refrigerant circuit comprises another sensor associated with the at least one evaporator; the method further comprising the step of: recording the signal indicative of power currently dissipated by the at least one evaporator using the other sensor. recording a first signal indicative of a thermodynamic state of the refrigerant using the first sensor; recording a second signal indicative of a thermodynamic state of the refrigerant using the second sensor; characterised in that the method comprises the steps of determining a first value of maximum available capacity of the refrigerant circuit as a function of the first and second signals; recording a third signal, the third signal being - a signal indicative of power currently dissipated by the at least one evaporator; - a signal indicative of power currently dissipated by the at least one evaporator; determining a first value of current capacity of the refrigerant circuit as a function of the third signal; determining a first ratio by relating the first value of current capacity to the first value of maximum available capacity; and if the determined first ratio exceeds one by a first threshold: producing a first alarm signal indicative of the loss of the refrigerant; further characterised in that the refrigerant circuit comprises another sensor associated with the at least one evaporator; the method further comprising the step of: recording the signal indicative of power currently dissipated by the at least one evaporator using the other sensor. producing a first alarm signal indicative of the loss of the refrigerant; further characterised in that the refrigerant circuit comprises another sensor associated with the at least one evaporator;