An emergency beacon includes a housing fitted with a connector for connecting the beacon to an antenna that is external to the housing. Inside the housing, the beacon includes an incident sensor, a transmitter, a detection and control member connected to the sensor and transmitter and arranged to trigger operation of the transmitter when an incident is detected. The beacon further includes, inside the housing, an incorporated antenna, a changeover switch interposed between the transmitter and the connector and also interposed between the transmitter and the incorporated antenna, and a sensitive member sensitive to the electromagnetic power conveyed towards the connector and to the electromagnetic power returned by the connector. The sensitive member is connected to the control member which is connected to the changeover switch and is programmed to deliver the signals from the transmitter to the external or incorporated antenna, depending on the state of the sensitive member.