What type of communication device may a signal person use in addition to hand signals?

The use of a walkie-talkie as a communication device in addition to hand signals is effective for several reasons. Walkie-talkies provide a reliable means of real-time communication over distances, which enhances coordination and safety on construction or industrial sites where visibility may be compromised or where loud machinery can drown out verbal communication. They allow the signal person to convey instructions clearly and immediately without having to be in close proximity to the equipment or workers, thus reducing the risk of misunderstanding that can occur with visual signals alone.

Other options like a cell phone may have limitations, such as poor reception in certain areas or the need for a continuous connection, which can be unreliable in dynamic environments. A whistle could serve as an auditory signal, but it may not convey specific instructions as clearly as radio communication. A flashlight can communicate in low light or during night operations, but it also lacks the immediacy and clarity of voice communication provided by a walkie-talkie. Thus, a walkie-talkie stands out as the most practical and efficient tool for enhancing communication in conjunction with hand signals in such settings.