Statusdroid
Statusdroid operates a worldwide network of servers which checks your website every 30 seconds from over 15 worldwide locations. If the website goes down, Statusdroid disables your PPC ads to prevent you from spending money on advertising that would take your customers to a dead end. It monitors not only availability of a website, but its security and response time as well. Statusdroid has integrated public status page which can send Facebook and Twitter message about any issue instead of you. You only need to provide addresses of your websites and Statusdriod automatically finds out what needs to be monitored. If there is something wrong, it will notify you via email, SMS or a phone call.
