Remote system up moniter

I have a number of remote systems each with a Web interface and local fixed IP. each connected to to a 4G router. These will send either an identified ping or even email which will sent/collected on a virtual cloud server say every 10 minutes. After 2 or 3 missed messages the server will email a list with a message that system X is off line. The server would then hold off further emails for x hours then repeat the message if communication is not reestablished. If comms is resumed it should then sent via the email list system x is on line again. Only 3 units for phase 1 trial