Bronze

Bronze is the internal mental pushing metal, and a Misting who burns it is called a Seeker. Burning bronze, an Allomancer feels other Allomancy being used nearby, less heard than felt, like a drumbeat somewhere close. The pulses give away roughly where the burner is and what metal is being used, since pushing metals wash over a Seeker while pulling metals tug at them ever so slightly, and internal metals give off longer pulses than external ones. A skilled enough Seeker can tell when an Allomancer is flaring a metal or running low on it. Copper is the answer to all of it, hiding Allomancy inside a cloud where a Seeker cannot feel it.