  Low Luminosity Active Galactic Nuclei (LLAGNs) are contaminated by the light
of their host galaxies, thus they cannot be detected by the usual colour
techniques. For this reason their evolution in cosmic time is poorly known.
Variability is a property shared by virtually all active galactic nuclei, and
it was adopted as a criterion to select them using multi epoch surveys. Here we
report on two variability surveys in different sky areas, the Selected Area 57
and the Chandra Deep Field South.
