  We adapt the friends of friends algorithm to the analysis of light curves,
and show that it can be successfully applied to searches for transient
phenomena in large photometric databases. As a test case we search OGLE-III
light curves for known dwarf novae. A single combination of control parameters
allows to narrow the search to 1% of the data while reaching a $\sim$90%
detection efficiency. A search involving $\sim$2% of the data and three
combinations of control parameters can be significantly more effective - in our
case a 100% efficiency is reached.
  The method can also quite efficiently detect semi-regular or strictly
periodic variability. We report 28 new variables found in the field of the
globular cluster M22, which was examined earlier with the help of
periodicity-searching algorithms
