Unknown devices

@user_3fa00b Hello! Thank you for reaching out to us here on our Community Forums. We certainly understand how important it is to ensure your in-home network is private and secure. If you rent a modem from us, we would certainly encourage you to visit this link (https://www.xfinity.com/support/articles/using-xfinity-xfi-advanced-security), here is where you'll find out how to enable Advanced Security to protect your network security. When you go to the site, scroll to the section labeled 'Enabling Advanced Security and follow the steps from here. You'll need to have the Xfinity app downloaded before you do the steps indicated. 

If you do not rent a modem from us, we would suggest changing your WiFI Network Password as soon as you can.

Xfinity advanced security will do nothing for your unknown device issue.  That's just a net nanny.  I'm surprised it was suggested.

There are a couple of things that can be happening. 

The mystery Apple device could be trying to connect to your network, but it isn't authenticating because it doesn't have the password.  Someone may have accidentally selected your WiFi network at some point while setting up someplace else, and it tries to connect sometimes, but fails.  They would have to "forget" your network to get it to stop.   Or if it is authenticating, getting an IP address, it's close by and your neighbor knows your WiFi password.  Likely your regular Xfinity password too if it keeps happening and that's where they are finding the WiFi password.  

The device will show up either way, but if it can't authenticate, it won't get an IP address, so it's not really on your network.

Change BOTH the WiFi password AND the Xfinity Account password at https://xfinity.com .  DO NOT USE your Xfinity account username or password at ANY other site -- Hulu or any other streaming service.  Password reuse is a horrid idea.  DO NOT USE an Xfinity email account for any other two factor or password recovery for ANY other site.   There are "other" reasons for that I won't get into here.

Another issue could be MoCA devices.  They are TCP/IP over coax.  You are supposed to have an MoCA Point of Entry filter installed where the coax comes into your house, but they often skip installing that part.  Other MoCA devices near by you can then connect without a password to your network.  There is no security on Xfinity's MoCA implementation.  You can buy one for less than $10 on amazon.  It just screws into the cable inline where cable enters, or if you don't have cable set top boxes, it can go right on the back of your gateway.  Then it blocks the signals from your neighbors house(s).   If a neighbor has an MoCA to Ethernet adapter, they may be connecting to your gear intentionally or unintentionally. 

A much better solution would be a 3rd party gateway that doesn't have the MoCA feature at all.  Then it's just not a problem.  Better still, is a cheap modem, a firewall appliance, then attach a 3rd party WiFi access point to that for your WiFi.  Take Xfinity right out of it.  Then NOBODY can see or configure your gear except for you locally, and there is no 3rd party website or phone app with configuration or WiFi information at all.  

if you have not had any resolution, this worked for me. Turn on your hotspot. When I did my 2.4 ghz network shut off and my phones connected to the hotspot. Shut off the hotspot and reconnect your phone to the network again. When I did this the unknown device disappeared completely, not in connected devices or disconnected devices.