The employer is paying you for the product, not the effort. I see no moral quandary here, nor any compulsion to notify the employer. They're getting what they want, that should be the end of it. EDIT: And I would add, for anyone that has automated their job in this way...what you should really be doing is scaling it up, and finding other companies who are probably paying employees to do the same thing. Then start you…
For those that might say that a job description sets product based terms for employment, it's rare that they are offered that way. Almost all the job descriptions that I've ever seen (and all that I've written) have some sort of phrase to the effect of, "...and other work as might be assigned." A job description isn't a Statement of Work, they're usually just general expectation setting devices.