You can make calls to the provided api for free and as often as you wish. :-).
However, please bare in mind that this is only hosted on a slow low-budget machine and I am doing this in my spare time. Once this service will be used frequently and the amount of donated coins allow it, I will move this page to a more powerful hosting contract.
There are also detailed api files for each timespan and each single site listed on the main page.
Click on one of the links on the main page to find them.
The remote party is always checked 5 times in a row with each of the following methods to prevent false positives and provide more reliable results.
If you are interested in the source code used to present this site, drop me a mail at: source[at] bitcoin-status [dot] org.