On Wed, 6 Feb 2019 19:04:09 -0000 (UTC), "Yes"
wrote:

Is there a CLI command I can use to identify what devices are currently
in use on my router (it has both ethernet and wi-fi)?

Not a Windows CLI command, but there are Linux-based tools that will
help. Google for 'penetration tools', for example. Looks like Kali might
be the current darling. https://tools.kali.org/tools-listing

I notice that the LED light for the wi-fi is very active even though
the two wi-fi devices I have (TV and cell phone) are turned off. I've
already looked at the web page for the router. It listed devices but
didn't seem to list what devices are currently using the wi-fi
connection.

From memory, I believe access points send a beacon about every 100
milliseconds to advertise their presence to clients in the area, so that
could look like activity. If you're concerned that someone has gained
access, just change the WiFi password. You'll have to update your two
WiFi devices. I assume you're already using at least WPA2 encryption,
right?

Are there other people in your nearby vicinity? I was going to say
especially people with time on their hands, but that's not a requirement
anymore. Tools for cracking WiFi passwords are fully automated these
days. It's no longer the manual methods we had 5-10 years ago.