As of version 2.6+ of Jetpack plugin, a WordPress website downtime and uptime monitoring feature was added. If you were paying a web service to monitor your WP website, using the free Jetpack monitor will save you that money.
Once activated, it will be checking your site every five minutes. If it looks like something’s gone awry (downtime), you will receive an email notification to the WordPress.com account that Jetpack is connected to. It’ll also let you know as soon as your site is up and running, so you can keep an eye on total downtime.
Few days ago when my blog had a downtime, I was swiftly notified by Jetpack monitor. I immediately contacted my host about the downtime and it was fixed.
If your WordPress blog is very important to you, you should start using Jetpack monitor.