How to get alert while CPU overused?

Are there any existing tools or application which can automatically send email when the CPU on server is overused? eg. CPU was more than 90% usage on a period of time or unusual CPU usage

You can do this with performance monitor (perfmon) out of the box in Windows. You can setup alerts on WMI counters with a threshold value, one of which can be total CPU.

The only tricky part is that it doesn't have an option to send emails (you can get it to send you a network message) but you can get it to run a command-line argument. You can use one of those command line mailer programs like blat to send an email.

For Windows I have used ServersAlive (link) before and found it to be a fantastic light weight tool.

Many other products exist Nagios, Microsoft System Center are two others that come to mind.

I had this same question a few months ago. I set up a performance alert using the built in windows tools. If it goes over the threshold, it fires off a vbs script that sends an email. Found the vbs script on google. Works great. I also only run it during hours I care about. No use having the blackberry buzzing away on the night stand unless it's a real emergency. Biggest drawback, no throttling. It keeps sending emails every time the alert fires. I keep thinking I'll dive into vbs and see if there's a way to limit it.

We use OpManager - great tool for monitoring server load, uptime, memory usage, etc... You can set up alerts based on thresholds so that you get an email if CPU goes over X, and a text message if CPU goes over Y. I think its free for up to 10 nodes.

I asked a similar question a few days ago and decided to try PRTG Network Monitor. I am not sure I am using it the most effective way but it was very easy to configure and it will send you email notifications when an alarm is triggered.

Try the "Free" edition, it has 10 sensors available, one of preconfigured ones is the CPU sensor, you just need to add an alarm trigger and configure the Notification service.

Good luck.

PRTG Network Monitor