Site24x7 or 24/7 monitoring of your sites

When you support several sites, I would like to know that a certain site has disconnected immediately and not several hours later from letters and calls from outraged users. And I would also like to somehow check which of the hosting providers, who standardly declare that “the sites on our hosting are available 24 hours a day, 7 days a week,” speaks the truth, and who plays a prank.

For this are the site monitoring services. One of the best is Site24x7 .
After registering your account, you can enjoy the full range of opportunities for 15 days, and after this period either stay on a free account that allows you to track two sites with certain restrictions, or pay extra for a professional account and monitor an unlimited number of sites in different more sophisticated ways.
This is what Site24x7 can do :

• Regularly send HTTP / HTTPS requests to your sites to check their performance. Requests are sent at intervals of 60 minutes for a free account, from 5 to 60 minutes (as set) for the professional.
  Track the response time of the site and report if it exceeds a certain specified amount.
  Record and regularly reproduce the test sequence of HTTP requests. It can be useful when checking the performance of trading systems, electronic stores, etc.
  Track changes to pages of sites. This means that you can set the percentage of page content changes, and when this percentage is exceeded, you will receive a message about it. Thus, you can catch unauthorized changes to the pages of your sites, various nasty Trojans, etc.
  Receive immediate notifications about the inaccessibility of the site, exceeding the permissible response time, changing the pages of the site and other events monitored by e-mail, as well as via SMS and RSS.
  Receive daily and / or weekly reports containing information about the availability / unavailability time of your sites for a given period, maximum, minimum and average access time and relevant charts.
  Of course, you can at any time, without waiting for the next report, go into your account and get all the necessary information there.
  Free and nice application - Tools in the Tools section - DNS and IP search by domain name (DNS Lookup and Find IP), checking availability of any site (Check Availability), and, finally, determining the real location of the site hosting with accuracy to the country and (not always) cities (Find Location).