In my previous role working within the Infrastructure Team, one of my specialisms was monitoring using Nagios Core. The great thing about Nagios is that many different plugins exist to allow you to monitor just about anything you can think of, and if a plugin doesn't exist for what you want, its a very simple task to create your own plugin to do the job.
This is what I ended up doing in order to monitor the status of our Denco air conditioning units in our datacentre.
I modified some Perl code to scrape the web status information and alert based on the output.
You can get the code from my GitHub repository here.