A monitoring appliance for detecting leaks of a refrigerant fluid from a refrigeration circuit of an industrial refrigeration system, comprising: - an electronic detection device for detecting leaks of a refrigerant fluid; - a body having a first portion for accommodating the electronic detection device for detecting leaks of a refrigerant fluid, said first portion being connected to an opposite second portion of the body, said second portion of the body comprising mechanical connection means configured to connect the monitoring appliance to an exhaust pipe (60; 70) of the refrigerant fluid, associated with at least one safety valve (40; 50) of the refrigeration system, wherein said electronic detection device comprises: - an optical oxygen sensor adapted to detect a decrease in an oxygen level below a first and a second preset threshold value inside the exhaust pipe, from a reference oxygen level value, caused by a leak of a refrigerant fluid from the safety valve (40; 50) into the exhaust pipe (60; 70); - an electronic control unit connected to said optical oxygen sensor; - an electronic status switching unit which can be activated by the electronic control unit to switch from a first to a second status to signal the detection of a decrease in the oxygen level in the exhaust pipe (60, 70) below said first or second preset threshold value, exceeding said first threshold value identifying a leak of a refrigerant fluid from the safety valve (40; 50) requiring the operating conditions of the valve to be monitored, exceeding said second threshold value identifying a leak of a refrigerant fluid from the safety valve (40; 50) requiring a valve replacement operation. - an electronic detection device for detecting leaks of a refrigerant fluid; - a body having a first portion for accommodating the electronic detection device for detecting leaks of a refrigerant fluid, said first portion being connected to an opposite second portion of the body, said second portion of the body comprising mechanical connection means configured to connect the monitoring appliance to an exhaust pipe (60; 70) of the refrigerant fluid, associated with at least one safety valve (40; 50) of the refrigeration system, wherein said electronic detection device comprises: - an optical oxygen sensor adapted to detect a decrease in an oxygen level below a first and a second preset threshold value inside the exhaust pipe, from a reference oxygen level value, caused by a leak of a refrigerant fluid from the safety valve (40; 50) into the exhaust pipe (60; 70); - an electronic control unit connected to said optical oxygen sensor; - an electronic status switching unit which can be activated by the electronic control unit to switch from a first to a second status to signal the detection of a decrease in the oxygen level in the exhaust pipe (60, 70) below said first or second preset threshold value, - an optical oxygen sensor adapted to detect a decrease in an oxygen level below a first and a second preset threshold value inside the exhaust pipe, from a reference oxygen level value, caused by a leak of a refrigerant fluid from the safety valve (40; 50) into the exhaust pipe (60; 70); - an electronic control unit connected to said optical oxygen sensor; - an electronic status switching unit which can be activated by the electronic control unit to switch from a first to a second status to signal the detection of a decrease in the oxygen level in the exhaust pipe (60, 70) below said first or second preset threshold value, exceeding said first threshold value identifying a leak of a refrigerant fluid from the safety valve (40; 50) requiring the operating conditions of the valve to be monitored, exceeding said second threshold value identifying a leak of a refrigerant fluid from the safety valve (40; 50) requiring a valve replacement operation.