  Ultralight dark matter (ULDM) particles of mass $m_\phi \lesssim 1~{\rm eV}$
can form boson stars in DM halos. Collapse of boson stars leads to explosive
bosenova emission of copious relativistic ULDM particles. In this work, we
analyze sensitivity of terrestrial and space-based experiments to detect such
relativistic scalar ULDM particles interacting through quadratic couplings with
Standard Model constituents, including electrons, photons and gluons. We
highlight key differences with searches for linear ULDM couplings. Screening of
ULDM with quadratic couplings near the surface of the Earth can significantly
impact observations in terrestrial experiments, motivating future space-based
experiments. We demonstrate excellent ULDM discovery prospects, especially for
quantum sensors, which can probe quadratic couplings orders below existing
constraints by detecting bosenova events in the ULDM mass range $10^{-23}\,{\rm
eV} \lesssim m_\phi \lesssim 10^{-5}\,{\rm eV}$. We also report updated
constraints on quadratic couplings of ULDM in case it comprises cold DM.
