What type of radio receiver scans several frequencies until it completes a message?

The type of radio receiver that scans several frequencies until it completes a message is known as a scanner. Scanners are designed to monitor multiple frequencies in order to pick up various types of communications, which can include emergency services, public safety communications, and other radio transmissions. This capability allows users to stay informed about different activities occurring on various channels without having to manually tune to each one. The scanning process involves the receiver rapidly cycling through the available frequencies and stopping momentarily when it detects a signal, thereby allowing it to pick up relevant information as it becomes available.

While simplex refers to a communication method where transmission happens in one direction at a time and does not involve multiple frequency scanning, a repeater is a device that amplifies signals to extend the communication range without directly scanning frequencies. Telemetry involves the automatic measurement and transmission of data from remote sources, typically not related to the concept of frequency scanning. Therefore, the functionality of a scanner is specifically tailored to meet the need for monitoring various frequencies concurrently, making it the correct choice in this context.