  The large majority of high energy sources detected with Fermi-LAT are
blazars, which are known to be very variable sources. High cadence long-term
monitoring simultaneously at different wavelengths being prohibitive, the study
of their transient activities can help shedding light on our understanding of
these objects. The early detection of such potentially fast transient events is
the key for triggering follow-up observations at other wavelengths. A Python
tool, FLaapLUC, built on top of the Science Tools provided by the Fermi Science
Support Center and the Fermi-LAT collaboration, has been developed using a
simple aperture photometry approach. This tool can effectively detect relative
flux variations in a set of predefined sources and alert potential users. Such
alerts can then be used to trigger target of opportunity observations with
other facilities. It is shown that FLaapLUC is an efficient tool to reveal
transient events in Fermi-LAT data, providing quick results which can be used
to promptly organise follow-up observations. Results from this simple aperture
photometry method are also compared to full likelihood analyses. The FLaapLUC
package is made available on GitHub and is open to contributions by the
community.
