NerdKey

Powered by NerdTools.co.uk Uptime Tracker (http://uptime.nerdtools.co.uk/) this plugin will add a widget to your sidebar that will show the percentage of availability or uptime for any website over the last 30 days.
In terms of the tracking system, checks are carried out every 5 minutes from different locations and then averages are worked out to form the overall reports from which the graph is generated and shown via an iframe.
Other reports including hourly, weekly and daily can be seen by visiting the Uptime Tracker website directly.
<h3>Arbitrary section 1</h3>

Uptime Widget

Adds a simple uptime gauge to your WordPress sidebar, showing the percentage of availability for any website over the past 30 days.

Frank Corso

SiteAlert

SiteAlert checks your WordPress installation to ensure that it is healthy, up to date, and secure. Use the SiteAlert page to quickly see the results of the checks using the simple color-coded sections.
Once installed, there will be a new SiteAlert page added to the Tools menu and heart icon to your admin bar if the results of these checks need attention.
Over 10,000 active installations and 280+ five star reviews!
<a href="https://sitealert.io/pricing" rel="nofollow ugc">Get instant alerts, premium performance monitoring, and more with our premium plan!</a>
<h4>Currently Checks</h4>
WordPress Version 
This plugin checks to make sure that your site is using the latest version of WordPress.
MySQL or MariaDB Version 
This plugin checks to make sure that your server is using a recent version of the database software.
PHP Version 
This plugin checks to ensure that your server is running a version of PHP that is still receiving security updates.
Plugin Updates 
This plugin checks to make sure all your plugins are up to date.
Inactive Plugins 
This will check to ensure that you do not have any inactive plugins.
Admin Username 
This check ensures that you do not have a user with the username of “admin” on your site.
Plugins No Longer Being Supported 
This plugin checks to see if you have any plugins installed that are no longer supported by the developer.
Theme Updates 
This plugin checks to make sure all of your themes are up to date.
SSL 
Checks to see if you have SSL on your site.
File Editor 
Checks if your site has disabled the file editor.
Spam Comments 
Checks to make sure you don’t have too many spam comments.
<h4>Need more?</h4>
Check out our affordable <a href="https://sitealert.io" rel="nofollow ugc">premium plan</a> that includes:
Email Notifications 
Receive summaries for all your sites including any warnings, broken links, and more!
Uptime Monitoring 
Get notified immediately via SMS or Email if your site goes down.
Page Speed Monitoring 
Keep track of how fast your site is loading.
Email Deliverability Monitoring 
SiteAlert will alert you if emails from your site are no longer being delivered.
Broken Link Monitoring 
Discover any broken links on your site before your visitors do.
Broken Images Monitoring 
Get notified if you have any broken images on your site.
Blacklist Monitoring 
SiteAlert will monitor dozens of lists and alert you if your site is blacklisted.
Moz Domain Authority Monitoring 
Monitor changes in your site’s Moz Domain Authority.
Alexa Rank Monitoring 
Monitor changes in your site’s Alexa Rank.
Accessibility Monitoring (Beta) 
SiteAlert will scan your site an alert you of potential accessibility concerns.
<a href="https://sitealert.io" rel="nofollow ugc">Learn more about our premium plan!</a>
<h4>Make Suggestions Or Contribute</h4>
SiteAlert <a href="https://github.com/SiteAlert/sitealert-wordpress-plugin" rel="nofollow ugc">is on GitHub</a>!
Optional REST API 
If you are a developer, this plugin integrates with the REST API. The endpoints can be enabled from the settings tab of the “SiteAlert” page in the tools menu.

SiteAlert (Formerly WP Health)

Peace of mind that your site is secure and running smoothly. Performance monitoring, security checks, and instant alerts if your site goes down.

Uptime Widget vs SiteAlert (Formerly WP Health)