This was a specific photometric mode integrating with the
C200
camera during slews in order to utilize the otherwise lost slew
time between ISO's pointed observations and thus increase the
overall observatory efficiency.
It was not a generally selectable observation mode. Serendipity Mode was
automatically activated by the Mission Planning software when a
slew was longer than 30 s. For slews longer than 70 s
an internal FCS measurement of 32 s was included. The
filter used for Serendipity Mode was the 170 
m filter,
the readout rate was fixed to a reset interval of 1/8 s.