is there a way to find out if someone is going on your wifi or using your wifi system
F-Secure SENSE apps provides you with this function and helps you monitor your secure home network.
From the SENSE app, tap on "Devices Protected", and on the next page you can see "Connected" and "Not Connected". By tapping on each device, you can "Block Internet (on this device)" if you suspect that device does not belong to your home. If you are able to identify your devices' IP and Mac addresses, that should help you narrow it down if there's an intruder on your network.