Certificates are typically valid for between 90 days and 1 year so you need to keep an eye on them and make sure they are renewed before they expire. An expired certificate is bad news, your browser doesn't pull any punches.
SiteSentry's SSL Certificate Expiration Check runs every day and verifies your site's certificate expiration date. If it's within the next 14 days it sends you a notification, so you have plenty of time to renew them.
Having a valid SSL certificate in place is a critical step to securing your site, but you also need to make sure that your visitors, and search engines, access your site securely. SiteSentry's HTTPS Redirect Check makes sure that visitors are redirected to the secure version of your site and let's you know if there's a problem.