Can I Tell Active Clients on RED Network?

So I want to be able to tell if a certain computer/device is active on a RED network. Can someone tell me what to do on the main ASG to see this.

I can only seem to determine if a DHCP lease was given to a certain IP or where I have given static IPs, neither of these show if the actual device is online or not.

Does this make sense, I want to see if a device on the RED network goes offline or verify that it is online?

Thanks