Another way is by network discovery tools like NMap. You scan the network and look for a machine/IP that isn’t assigned to any of your existing machines. I wouldn’t recommend this though in a professional/working environment, since it can raise some flags – either on AVs or if your network is monitored.
This technique is also used to discover vulnerabilities – that’s the reason I recommend using it only in a personal or developing environment.
The best and safest approach is the one that Jeff proposed.
Best regards.