Wasitup? is a website that allows you to monitor your website’s uptime and notifies you via email whenever your site is down. You can monitor up to 10 websites at once painlessly using “Manage Monitorings” and the best part is that no registration is required to use this service. Just visit the site, enter your site’s address and your email ID. The three fields that you have to fill in include one in which you provide the name of the site (“Make sure this site is up”), another one where you specify what the application must look out for, and a final section in which you set down the contact e-mail to be used for notification purposes.
Wasitup? performs an HTTP HEAD request and checks that the status code is 200 OK. Your website is polled every 5 minutes.
WasItUp is very useful, free. No doubt, a tool that every webmaster should use.