Biotelemetric device integrable within a biocompatible capsule and intended for use in a biological environment after ingestion or in vivo implantation, to be used in conjunction with an external device, the biotelemetric device comprising: - a microcontroller configured to generate an electrical setpoint signal; - a radio antenna configured to transmit at least an electromagnetic wave by converting an incident electrical signal, in order to transmit data to said external device via a radio connection with said external device; - a radio frequency circuit, interconnected between the microcontroller and the radio antenna, the radio antenna being configured to, when the biotelemetric device is placed in the biological environment, be impedance mismatched with respect to the radio frequency circuit so as to generate a reflected electrical signal by reflection of a fraction of the incident electrical signal while the radio antenna emits the electromagnetic wave; in which the radiofrequency circuit is configured to take a first fraction of the electrical setpoint signal, transmit to the radio antenna a second fraction of the electrical setpoint signal forming the incident electrical signal and take the electrical signal reflected by the radio antenna; in which the microcontroller is configured to determine, relative to the first fraction of the electrical setpoint signal, a reflection coefficient (S 11) corresponding to the fraction of the electrical signal reflected by the radio antenna. - a microcontroller configured to generate an electrical setpoint signal; - a radio antenna configured to transmit at least an electromagnetic wave by converting an incident electrical signal, in order to transmit data to said external device via a radio connection with said external device; - a radio frequency circuit, interconnected between the microcontroller and the radio antenna, the radio antenna being configured to, when the biotelemetric device is placed in the biological environment, be impedance mismatched with respect to the radio frequency circuit so as to generate a reflected electrical signal by reflection of a fraction of the incident electrical signal while the radio antenna emits the electromagnetic wave; in which the radiofrequency circuit is configured to take a first fraction of the electrical setpoint signal, transmit to the radio antenna a second fraction of the electrical setpoint signal forming the incident electrical signal and take the electrical signal reflected by the radio antenna; in which the microcontroller is configured to determine, relative to the first fraction of the electrical setpoint signal, a reflection coefficient (S 11) corresponding to the fraction of the electrical signal reflected by the radio antenna. the radio antenna being configured to, when the biotelemetric device is placed in the biological environment, be impedance mismatched with respect to the radio frequency circuit so as to generate a reflected electrical signal by reflection of a fraction of the incident electrical signal while the radio antenna emits the electromagnetic wave; in which the radiofrequency circuit is configured to take a first fraction of the electrical setpoint signal, transmit to the radio antenna a second fraction of the electrical setpoint signal forming the incident electrical signal and take the electrical signal reflected by the radio antenna; in which the microcontroller is configured to determine, relative to the first fraction of the electrical setpoint signal, a reflection coefficient (S 11) corresponding to the fraction of the electrical signal reflected by the radio antenna.