A common form of turning in a fire alarm is by using:

The correct answer highlights the telephone system as a common method for reporting or turning in a fire alarm. The telephone system is widely utilized because it allows immediate communication to emergency services, ensuring a timely response when a fire incident is suspected or detected. This method streamlines the process of alerting emergency responders, providing them with essential information quickly.

Using the telephone to report fires is advantageous due to its reliability and familiarity among the public, as most individuals know how to use a phone to communicate emergencies. This method can also facilitate direct contact between the caller and the dispatch center, allowing for the gathering of critical details about the location and nature of the incident.

Other forms such as radio fire alarm boxes and walkie talkies might not be as commonly used for direct reporting by civilians, as they may require specialized training or equipment not available to the general public. Walk-in contact, while conceptually valid, is not practical for immediate reporting in emergencies compared to the ubiquitous nature of telephone systems. Thus, the telephone system stands out as the most common and effective way for reporting fire alarms.