How can I find out if someone uses my wifi without my permission?

[atari]

I have my wifi and live in an apartment building. I want to check if someone is connected to me and using my internet connection.

How can I do that?

[mod]

If you work with Windows computer, I'd suggest taking a look at the Netstumbler (see here http://www.maxi-pedia.com/download+netstumbler).

If you work in Linux, try aircrack-ng.

In both cases, know that you will need to set your network interface card into so-called monitor mode. I think, Netstumbler is capable of doing this for you. With aircrack-ng, you will need to do some configuration. See the following two links for more details on related stuff

http://www.maxi-pedia.com/crack+WEP
http://www.maxi-pedia.com/how+to+crack+WEP+with+intel+PRO+wireless+3945ABG

[Pansophic]

If you work with Windows computer, I'd suggest taking a look at the Netstumbler (see here http://www.maxi-pedia.com/download+netstumbler).

If you work in Linux, try aircrack-ng.

In both cases, know that you will need to set your network interface card into so-called monitor mode. I think, Netstumbler is capable of doing this for you. With aircrack-ng, you will need to do some configuration. See the following two links for more details on related stuff

http://www.maxi-pedia.com/crack+WEP
http://www.maxi-pedia.com/how+to+crack+WEP+with+intel+PRO+wireless+3945ABG

i think this is the most accurate answer and it also helped me