Uptime Robot - Checking Whether Your Site Is Reachable at 5-Minute Intervals
Uptime Robot is an uptime monitoring service that I personally recommend. It checks whether your server is running and whether visitors can actually reach your website. Many services are similar to Uptime Robot, but most free uptime monitoring services only check every hour or less (in other words, how often the service checks your site). Uptime Robot's shortest interval is 5 minutes, and if it detects a problem with your site, it automatically sends you an email. Uptime Robot is free for now, but I'm not sure whether it will charge later......