The Hardware Dashboard in the Control Center indicates when an ACU is offline by highlighting the row in red. To receive alerts when the ACU goes offline, see How do I set up alerts?
If your ACU is offline, try the following:
Check that all network requirements are met: Network Requirements for Openpath
Check that the Ethernet cable is securely connected to the ACU and to the switch, router, or modem
Unplug the Ethernet cable from the ACU and plug it into a laptop to check if there is Internet service
Check the status LED: What do the LEDs on ACUs/SDCs mean?
Use the Remote Diagnostics tools in the Control Center: How do I troubleshoot ACUs and Smart Readers?
Reboot the system by unplugging the ACU from power. Wait 30 seconds before plugging the power back in. Wait a few minutes before checking the Hardware Dashboard.
Note: You may need to refresh the page to see if the ACU changed from offline to online