File integrity monitoring/IPS?

Is there a service or technique for doing file integrity monitoring on a website?

For example, if my index.html page changes, I want an email or text sent to me.

Near as I can tell, this is not a service offered by Dreamhost, but I sorta’ figure someone out there is offering such a thing.
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I’m not talking about uptime/downtime – I’m talking about if someone actually modifies a file (such as our home page).

You can create a crontab job with a php/bash script to monitor the modified time of the index.html file. If it is changed, send an email to yourself.

Well…

I’m looking at something that’s not susceptible to the same issues as the environment. Sure, there’s a decent chance a malicious attacker might not think to kill any cron jobs, but something that monitors the file and is not on the same attack surface as the domain would be preferable.