Process definition

This solution isn't "pretty" :-)

Set a parallel path, one with "wait 30 days" which would move to whatever action you want, and a second path with a receive message set for "Date Modified changes" that would progress to the next step - which might be to just terminate the process.

Thank you Bud for you reply, the problem I see with this is that it will execute the process whether or not the date of last modification changed. It is an alert for the user, if the last modification date of the record does not change in 30 days , an email is sent informing that there were no changes in that record for a month

Thank you Bud for you reply, the problem I see with this is that it will execute the process whether or not the date of last modification changed. It is an alert for the user, if the last modification date of the record does not change in 30 days , an email is sent informing that there were no changes in that record for a month

That is correct.  I said it wasn't "pretty".  You will have the process running for each record.  Depending on which happens first (30 days or a modification) the next step will be executed.  If the record is modified, you will need to terminate the process, if the 30 days pass you should terminate the process after the email is sent.