Check for unwanted users on my wifi

[ramelthecamel]

How do I check for unwanted devices logged into my WiFi modem. When I log into my modem there is no tab or link to check which devices are connected. 

[schumaku]

The tagged CM500 is a pure modem, not providing any routing or WiFi access. 

[ramelthecamel]

So what is another way I can check for unwanted users if I can't check through my modem?

[schumaku]

Figure out what is providing the wireless access for your LAN. Look out where the one and only Ethernet port (the yellow marked RJ45) connected cable is heading to ...

Double check the cable device is really a Netgear CM500 

Next approach would be to change the wireless network password/security passphrase.and re-configure your wireless clients (mobile, computer, printers, IoT, ...) - but to make this happen you need to figure out what is delivering your wireless access.