Networks

Keep the tinfoil handy...meanwhile, it would appear that your modem is assigned
one of the IP addresses and probably a router for the other, along with your
smartphone. If you enabled WEP and picked a pretty decent password, your
WiFi network should be ok, but if you left it open, then a neighbor could be
piggy-backing on your WiFi.

That's what you just said. Maybe you could clarify what you are seeing.

Are the connections active? Many routers keep track of devices previously connected, as well as everything currently connected.

Following article describes how to know if someone is watching you on Internet:

http://www.tekgazet. com/will-my-boss-monitor-internet-use/net/22.html