Character design question: is this superpower too weak? Too strong? Utterly useless? Details in the details section.

The setting is a sort of sci-fi/fantasy hybrid – weird science, maybe; I’ll see what TvTropes has to say later. Technology is more or less 1920s-1940s
The character in question (a second-tier protagonist) has the ability to sense electromagnetic fields, and the fluctuations in them; the sense is acute enough to detect, say, Morse code over a line, but (probably?) not enough to be able to “overhear” telephone conversations.
I decided that I didn’t want a power-driven plot, preferring instead to focus on travel, trade, and exploration.