Created a script that will fail.
Created Smart Filter to show all script log events with Had Error = true over the past day.
Created trigger "Alert on script error" on insert and update for the Smart Filter.
Set trigger action to send me an email.
This approach to alerting for script execution failures doesn't work because some records, including Script Logs, act different: they are 'system generated' -- thus they don't trip triggers.
The expected behaviour is for all records to be able to initiate triggers.