monitoring a single dedicated server

For those of you with an unmanaged dedicated server (with no monitoring by the datacenter/NOC), does anyone have a good way to monitor it to notify you if it goes offline? For example a free or low cost Windows program you can run locally which checks every 5, 10, or 15 minutes to see that everything is up and beeps or in another way lets you know as soon as the server has a problem?

 

 

 

 

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