It works as an internal plugin that listens to all issue events (update, status update etc..).
For each event it will insert a detailed record into the alerts table with the alert code and the previous issue stored in alert data as binary.
Does this help?

yes, i had a feeling thats what it did which is just want i need, but when does it get cleaned out?

And is it safe to put a trigger on this table?

Oh and one more question i seem to have some old data in that table is it ok to remove it (dates back to about a month ago)?

Forgot to mention that the table will only get populated if you are using the scheduler service for email alerts. The scheduler will delete records as it process the alerts.

You may clear old data as it is probably due to deleted issues.
If you are putting triggers on the table make sure to set nocount to on.