  Microscopic horizonless relics could form in the early universe either
directly through gravitational collapse or as stable remnants of the Hawking
evaporation of primordial black holes. In both cases they completely or
partially evade cosmological constraints arising from Hawking evaporation and
in certain mass ranges can explain the entirety of the dark matter. We
systematically explore the stochastic gravitational-wave background associated
with the formation of microscopic dark-matter relics in various scenarios,
adopting an agnostic approach and discussing the limitations introduced by
existing constraints, possible ways to circumvent the latter, and expected
astrophysical foregrounds. Interestingly, this signal is at most marginally
detectable with current interferometers but could be detectable by
third-generations instruments such as the Einstein Telescope, strengthening
their potential as discovery machines.
