  Planck LFI (Low Frequency Instrument) will produce a complete survey of the
sky at millimeter wavelengths. Data stream analysis will provide the
possibility to reveal unexpected millimeter sources and to study their flux
evolution in time at different frequencies. We describe here the main
implications and discuss data analysis methods. Planck sensitivities typical
for this kind of detection are taken into account. We present also preliminary
results of our simulation activity.
