Looking for software to notify me when a computer on my network loses internet connection

Hi all,

We use teamviewer at my work for remote control for all of our users. Teamviewer has a little pop up window that will flash on the screen when a user in our list turns their computer on, showing that it is now online. Every so often we will see an entire section of one of our plants pop online, this tells us that there was possibly a fault in the switch feeding that area - this is nice to be able to see but it does not tell us how long the internet has been out in that area, just when it came back online.

Have any of you used any software that could notify me as soon as a computer drops off the network?

Thank