Please review our project SiteCanary
kiwidrew: It's a really clean site that feels responsive (even from .nz) and isn't too cluttered -- great work!A few bits of feedback:
 - When I was adding a new site to check, it wasn't immediately clear whether you support sending text messages to non-US mobiles.  The only example provided is formatted US-style (1-xxx-xxx-xxxx).  I put in my NZ mobile as 6421xxxxxxx and it did in fact work.  I'd suggest adding a second example number formatted as e.g. +44xxxxxxxxx and perhaps a link to a page listing the countries you support.
 - Perhaps an option to send a second text message when the site comes back up?
 - The subject line of the email which is sent when the site comes back up is simply 'SiteCanary: accountname:'.  It'd be good to have this be 'SiteCanary: sitename is back!' instead.