You can also use Google Docs to monitor your website(s) and, unlike the commercial services, Google imposes no restrictions. You can track any number of websites with Google Docs and it will send email /text alerts in case of any issues. And this DIY website monitoring tool is absolutely free.
This is so awesome. It’s well worth setting it up, it takes only a few moments and you can then just forget about it.
SMS notifications don’t seem to be supported in the UK so instead I’ve set this up to use with Pushover, a great push notification platform that provides the ability to trigger notifications on your iPhone via email (or using their API with services such as IFTTT). All Pushover accounts get a unique email address that can be used to trigger notifications which I’ve used within the Google Docs document.