Detectify - Detectify provides a user friendly and thorough web security scan that allows you to focus 100% on web development.
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.
Burp Suite - Burp Suite is an integrated platform for performing security testing of web applications.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Vulmon Alerts - Vulmon Alerts provides vulnerability notification service. Vulmon Alerts is how you proactively detect vulnerabilities. Subscribe to any query related to vulnerabilities and get alerted before hackers.
Better Uptime - We call you when your website goes down