Website Uptime Monitor?

Free website monitoring service: Montastic

^_^

When running a company's data center (single homed - ie just one DC) I've used Keynote's red alert service:
Web Site Monitoring by Keynote Red Alert
and was very happy with them.

I used several services, not just the up/down monitoring - things like database access, username/password access etc. Just remember to de-activate the monitoring before doing any system maintenance.

If you run a few servers (dedicated) on different networks in different Data centers, and either understand Linux system administration or have access to a sys admin, check out nagios (formerly netsaint). You don't want to run this on just one computer, or separate computers in the same network.

I've also ran a program called What's Up Gold on Windoz machines, it was ok, but don't even know if its still available. I would go with Nagios before it though.

All will typically send email to any email enabled device. But you have to be careful - a network error can cause a cascade and you might get hundreds of messages - when only one is needed. If you're on a limited data plan that can eat up some bytes.

And if you think monitoring services are expensive, you should see the costs of things like smarts, openview, nervecenter, netcool(although its been a while and some of these names are actually the same family of programs now through all the mergers etc). The prices for such installation run into the hundreds of thousands of $$$$.

Good luck.
--Jack