This paper reports on a qualitative study on the weakest flarelike brighten
ings in active region that can be observed with current coronal imagers. Sp
ecificallly, we investigate the correspondence of the "active region transi
ent brightenings" (ARTB) first observed almost a decade ago with SXT with s
imilar brightenings in the EUV that are now observed by EIT and TRACE. For
this goal, exceptionally high cadence image sequences were acquired of a sm
all but rapidly evolving active region (NOAA 8218), simultaneously by SXT,
EIT, and TRACE. Within the timeframe of this coordinated campaign, we detec
ted 41 soft X-ray brightenings and 373 EUV brightenings. We find that the s
trongest brightenings observed by EIT are indeed the EUV counterparts of th
e ARTBs seen by SXT. Weaker brightenings seen by EIT often do not have an X
-ray counterpart. Among the brightenings detected with SXT we discover a ne
w subpopulation, consisting of events that brighten in soft X-rays only, at
a footpoint of a pre-existing SXT loop shortly after an ARTE occurred at t
he other footpoint. The propagation speed of the perturbation suggests an i
nterpretation in terms of slow mode MHD waves.