Pingdom also provides free web monitoring service.
This is free but powerful service, it provides premium services also. It works 24 hours of a day.
This checks your website every 30 minute’s interval and reports you if your site goes down.
If you have a free account, it will monitor your site for every 60 minutes.
It is also free and alerts you via email or SMS.
It is a pure website uptime monitoring site.
This service is free for first 90 days after it will cost 1$/month for every hour checking of your sites p or down time.
I think this service is completely free for web monitoring.
It is server monitoring service, for one server it is free if you have more than one server it will cost you.
It is a free ; it will notify you when your website goes down.
It is also a uptime monitoring site.