  Large time-domain surveys provide a unique opportunity to detect and explore
variability of millions of sources on timescales from days to years. Broadband
photometric variability can be used as the key selection criteria for weak
type-I active galactic nuclei (AGN), when other "direct" confirmation criteria
like X-ray or radio emission are unavailable. However, to detect variability of
rather weak AGN powered by intermediate-mass black holes, typical sensitivity
provided by existing light curve databases is insufficient. Here we present an
algorithm for post-processing of light curves for sources with stochastic
variability, retrieved from the The Zwicky Transient Facility (ZTF) Forced
Photometry service. Using our approach, we can filter out spurious data points
related to data reduction artefacts and also eliminate long-term trends related
to imperfect photometric calibration. We can now confidently detect the
broad-band variability at the 1-3 $\%$ level which can potentially be used as a
substitute for expensive X-ray follow-up observations.
