Measurement device for a monitoring system intended to be installed in an aircraft, the measurement device being designed to operate according to a first operating mode, referred to as the "on the ground" operating mode, or a second operating mode, referred to as the "in flight" operating mode, the measurement device comprising: - a sensor designed to measure at least one physical parameter of the environment of the aircraft, - a radio module in accordance with a low-power wide-area network standard, the radio module being designed to transmit messages comprising measurement data originating from the sensor to a radio access point, the radio module being designed to transmit each message with a transmission power chosen from among a predefined plurality of transmission powers, - an electrical power supply source, - a module for managing the electrical power supply, connected in stream between the radio module and the electrical power supply module, - a control module, the control module being designed to switch the operating mode of the measurement device between the first operating mode, referred to as the "on the ground" operating mode, and the second operating mode, referred to as the "in flight" operating mode, the measurement device being characterized in that the module for managing the power supply comprises an energy storage element making it possible to supply power to the radio module; and the measurement device is designed to: - in the first operating mode, referred to as the "on the ground" operating mode: o before transmitting each message, charge the energy storage element with a predefined amount of energy delivered by the electrical power supply source, - in the second operating mode, referred to as the "in flight" operating mode: o for each message to be transmitted, choose a transmission power of the radio module, o determine, depending on this transmission power, an amount of energy necessary for transmitting the message by means of the radio module, o before transmitting the message, charge the energy storage element with the determined necessary amount of energy delivered by the electrical power supply source. - a sensor designed to measure at least one physical parameter of the environment of the aircraft, - a radio module in accordance with a low-power wide-area network standard, the radio module being designed to transmit messages comprising measurement data originating from the sensor to a radio access point, the radio module being designed to transmit each message with a transmission power chosen from among a predefined plurality of transmission powers, - an electrical power supply source, - a module for managing the electrical power supply, connected in stream between the radio module and the electrical power supply module, - a control module, the control module being designed to switch the operating mode of the measurement device between the first operating mode, referred to as the "on the ground" operating mode, and the second operating mode, referred to as the "in flight" operating mode, the measurement device being characterized in that the module for managing the power supply comprises an energy storage element making it possible to supply power to the radio module; and the measurement device is designed to: - in the first operating mode, referred to as the "on the ground" operating mode: o before transmitting each message, charge the energy storage element with a predefined amount of energy delivered by the electrical power supply source, - in the second operating mode, referred to as the "in flight" operating mode: o for each message to be transmitted, choose a transmission power of the radio module, o determine, depending on this transmission power, an amount of energy necessary for transmitting the message by means of the radio module, o before transmitting the message, charge the energy storage element with the determined necessary amount of energy delivered by the electrical power supply source. - in the first operating mode, referred to as the "on the ground" operating mode: o before transmitting each message, charge the energy storage element with a predefined amount of energy delivered by the electrical power supply source, - in the second operating mode, referred to as the "in flight" operating mode: o for each message to be transmitted, choose a transmission power of the radio module, o determine, depending on this transmission power, an amount of energy necessary for transmitting the message by means of the radio module, o before transmitting the message, charge the energy storage element with the determined necessary amount of energy delivered by the electrical power supply source. o for each message to be transmitted, choose a transmission power of the radio module, o determine, depending on this transmission power, an amount of energy necessary for transmitting the message by means of the radio module, o before transmitting the message, charge the energy storage element with the determined necessary amount of energy delivered by the electrical power supply source.