If your system(s) are compatible with any of these, deploy those sensors and then set-up alerts based on a lower limit, for instance set the sensor to down when the uptime is less than 600 seconds and into warning when the uptime is less than 900 seconds. You can use this together with notifications if you wish to be notified.
Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.