  We aim to investigate the temperature enhancements and formation heights of
impulsive heating phenomena in solar active-regions such as Ellerman bombs
(EBs), ultraviolet bursts (UVBs), and flaring active-region fibrils (FAFs)
using interferometric observations in the millimeter (mm) continuum provided by
the Atacama Large Millimeter/submillimeter Array (ALMA). We examined 3 mm
signatures of heating events identified in Solar Dynamics Observatory (SDO)
observations of an active region and compared the results with synthetic
spectra from a 3D radiative magnetohydrodynamic simulation. We estimated the
contribution from the corona to the mm brightness using differential emission
measure analysis. We report the null detection of EBs in the 3 mm continuum at
$\sim1.2$" spatial resolution, which is evidence that they are sub-canopy
events that do not significantly contribute to heating the upper chromosphere.
In contrast, we find the active region to be populated with multiple compact,
bright, flickering mm bursts -- reminiscent of UVBs. The high brightness
temperatures of up to $\sim14200$ K in some events have a significant
contribution (up to $\sim$7%) from the corona. We also detect FAF-like events
in the 3 mm continuum that show rapid motions of $>10000\,$K plasma launched
with high plane-of-sky velocities ($37-340\rm\,km\,s^{-1}$) from bright
kernels. The mm FAFs are the brightest class of warm canopy fibrils that
connect magnetic regions of opposite polarities. The simulation confirms that
ALMA should be able to detect the mm counterparts of UVBs and small flares and
thus provide a complementary diagnostic for localized heating in the solar
chromosphere.
