Rogue Device on Network

I was looking at the DHCP client list last night, and I noticed a device that I didn't recognize. It listed its host name as android-<mac addrress>. I don't have any android devices. I did not see this device listed in the Unifi Client List.

My setup is Edgerouter POE -> EdgeSwitch Lite -> CloudKey -> 2 Unifi Access Points.

1. If a wireless device comes into range, will the router assign an IP address even if the device isn't allowed on the wireless network?
2. How might I track down this device?
3. Should I be unconcerned or greatly alarmed that someone entered my house to access the physical network?

Thanks for any thoughts and feedboack on how I might proceed.

Jeff