  We study the symmetry requirements for topologically protected spin-polarized
Weyl points in 2D altermagnets. The topology is characterized by a quantized
$\pi$-Berry phase and the degeneracy is protected by spin-space group
symmetries. Gapped phases with finite Chern and/or spin/chirality Chern numbers
emerge under different symmetry-breaking mass terms. We investigate the surface
and transport properties of these gapped phases using representative electronic
tight-binding and magnonic linear spin-wave models. In particular, we calculate
the electronic and magnonic Hall currents and discuss implications for
experiments.
