When you need to know that the site is up and running
- pingdom.com/free/
- uptimerobot.com
- statuscake.com
- serviceuptime.com
- siteuptime.com
- pingometer.com
- www.host-tracker.com
- site24x7.com
- https://www.websiteplanet.com/webtools/down-or-not/
** wordpress sites depend on site visits for cron and some updates are triggered on a cron run so for a site that gets low traffic pinging (BASE URL)/wp-cron.php can help