PeoplesGeek

Monitoring services like www.siteuptime.com or www.montastic.com require a page on your website to monitor.
This plugin provides a virtual target for your monitoring services that does not invoke other plugins (specifically avoiding the Google analytics plugins so that your statistics are not skewed by monitoring calls) 
The two targets provided for the monitoring service are:
<ul>
<li>monitor.htm – via .htaccess and does not use WordPress (but does use PHP)</li>
<li>monitorWP.htm – via WP and so tests the Database etc is working</li>
</ul>

PG Monitor

A virtual target file to be read by monitoring services instead of using a static HTML page.

Edward Stoever

Imagine opening your mobile device and immediately viewing messages sent from your WordPress server with important information about what is happening right now. Stay informed on uptime, downtime, backups, memory usage, disk usage, intrusion attempts, sign-ups, or anything that matters to you!
With the Monitor.chat plugin, you will stay informed about:
<ul>
<li>Logins, including failed login attempts</li>
<li>New posts</li>
<li>New comments</li>
<li>Software updates including core, plugins, and themes</li>
<li>File system space available</li>
<li>Server memory usage</li>
</ul>
The Monitor.chat plugin will notify you by instant message on events and scheduled reports from the following plugins:
<ul>
<li>Akismet Anti-Spam</li>
<li>Updraft Backups</li>
<li>Gwolle Guestbook</li>
<li>Woocommerce</li>
<li>WP-Statistics </li>
</ul>
The Monitor.chat plugin relies on an external service. Messages are posted by the Monitor.chat plugin along with an API key to an external server. The external server converts the API key into the correct recipient(s) and sends the message as an XMPP instant message. 
* Website: https://monitor.chat 
* Policies of Monitor.chat: https://monitor.chat/documentation/policies/

Monitor.chat – Monitor WordPress with Instant Messages

Your WordPress server will keep you informed in real-time with instant messages that you receive on your mobile device.

PG Monitor vs Monitor.chat – Monitor WordPress with Instant Messages