Detecting when field value changes in Foreign Table?

I have an oracle foreign table that holds arbitrary tasks, when a task gets updated the "time_update" field will
change.I want to detect when the field changes so I can insert the values in a local table for completed tasks. Can
postgresqldetect changes in a foreign table so a trigger can be invoked? I am new to postgrwsql so any examples or
educationon what steps to take to complete tjos would be greatly appreciated! <br /><hr align="left" width="300" />
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