I use HomeSeer's JSON interface. For example:

http://IP Address/JSON?request=getstatus&ref=#

For details and example output see:

[Link: homeseer.com]

I'm not familiar with HomeSeer_REST_API.aspx (and not sure why to use it since HomeSeer has the aforementioned JSON API, unless maybe it precludes the need to parse the JSON response?).

But either way, the idea would be to use http similar to what was mentioned in:

[Link: remotecentral.com]

Then, once you've extracted the status value you want, do as Lyndel mentioned.