What technology is used to convert electronic signals into coded audible signals for transmission?

Telemetry is the correct choice because it refers to the use of electronic devices to measure and transmit data remotely. In the context of emergency medical services, telemetry allows for the conversion of electronic signals—such as vital signs measured by medical devices—into coded audible signals that can be transmitted over radio frequencies. This technology is essential for efficiently sending patient information from the site of an emergency to medical facilities, allowing for timely decisions to be made regarding the patient's care.

The other options do not serve this specific function. Simplex radio is a type of radio communication that allows transmission in one direction at a time, but it does not specifically involve converting electronic signals into coded audible ones. A repeater is used to extend the range of radio signals by receiving and retransmitting them but doesn't itself convert signals into readable or audible formats. Lastly, a scanner refers to a device that can monitor multiple channels but does not perform the function of converting signals for transmission. Thus, telemetry is distinct in its capability to handle the specific task of electronic signal conversion for audible transmission in medical contexts.