User expresses concerns about unauthorized devices and potential spying on their guest network, even with separate credentials. They seek recommendations for monitoring and catching intruders, implying a need for enhanced security features.
There are many more security settings that you haven't mentioned. Basically any device that connects to the wireless could be a compromised device. I set up a guest Network with different credentials than the main wireless network. The even with this it seems somehow problems arise. I found about 13 generation devices on the guest Network. There is only supposed to be one at this time. There are no wireless IP cameras or smart devices connected to this wireless guest Network. If there is a guest that uses the guest network from time to time which is untrusted with some knowledge of i.t. how could they remotely spy on the network or put devices in the house such as listening or video recording and using the Wi-Fi to spy? I know they can do this remotely and try to crack the password if they can find the MAC address and take away the colons I've heard. If true this would be how they are logging in into the router interface. I want to catch this person in the act what recommendations would you have for this task?