  Surface Fermi arcs are the most prominent manifestation of the topological
nature of Weyl semimetals. In the presence of a static magnetic field oriented
perpendicular to the sample surface, their existence leads to unique
inter-surface cyclotron orbits. We propose two experiments which directly probe
the Fermi arcs: a magnetic field dependent non-local DC voltage and sharp
resonances in the transmission of electromagnetic waves at frequencies
controlled by the field. We show that these experiments do not rely on quantum
mechanical phase coherence, which renders them far more robust and
experimentally accessible than quantum effects. We also comment on the
applicability of these ideas to Dirac semimetals.
