  Magnetically charged black holes (MBHs) are interesting solutions of the
Standard Model and general relativity. They may possess a "hairy"
electroweak-symmetric corona outside the event horizon, which speeds up their
Hawking radiation and leads them to become nearly extremal on short timescales.
Their masses could range from the Planck scale up to the Earth mass. We study
various methods to search for primordially produced MBHs and estimate the upper
limits on their abundance. We revisit the Parker bound on magnetic monopoles
and show that it can be extended by several orders of magnitude using the
large-scale coherent magnetic fields in Andromeda. This sets a mass-independent
constraint that MBHs have an abundance less than $6 \times 10^{-3}$ times that
of dark matter. MBHs can also be captured in astrophysical systems like the
Sun, the Earth, or neutron stars. There, they can become non-extremal either
from merging with an oppositely charged MBH or absorbing nucleons. The
resulting Hawking radiation can be detected as neutrinos, photons, or heat.
High-energy neutrino searches in particular can set a stronger bound than the
Parker bound for some MBH masses, down to an abundance $10^{-7}$ of dark
matter.
