If you're comfortable at the CLI, WPScan is super easy to get going. The project is open source on Github and uses the WPScan Vulnerability Database, an open dataset of known WordPress vulnerabilities. Installation on a Mac is a piece of cake. Other methods and operating systems are documented on Github.
Uptime and SSL certificate monitoring doesn't have to be boring, confusing or expensive. Together with my buddy Mattias Geniar I'm currently building Oh Dear: a webapp to keep an eye on the health of your websites. Register here to try it out. (sponsored link)