Wireless home networks are so popular, so security is an important matter.
Firstly you can check if someone is connecting to home network without being authorized.From the router admin panel see the list of connected devices.
The security measures that you can do:
– change router default password
– setup a more strong wireless key encryption (eg. WPA2 instead of WEP and WPA)
– change default wireless key
– filter MAC addresses (you can choose which devices are granted by listing their MAC, the physical address of network devices)