AWS WAF - AWS WAF is a web application firewall that helps protect your web applications from common web exploits.
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
ModSecurity - ModSecurity is an Open Source web application firewall developed by Trustwave's SpiderLabs.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Barracuda Web Application Firewall - Barracuda Web Application Firewall offers security and DDoS protection against automated & targeted attacks.
Better Uptime - We call you when your website goes down