Aircrack-ng is a program and specialized in cracking passwords 802.11 WEP and WPA-PSK, which can also be used for normal activities of hacking, one of which is for example to verify the presence of Wi-Fi networks reachable through the your router.
To use this application on Linux are sufficient number of simple commands from Shell, for example in Ubuntu you can install it with the statement:
<span onmouseover="_tipon(this)" onmouseout="_tipoff()"><span class="google-src-text" style="direction: ltr; text-align: left;">sudo apt-get install aircrack-ng</span> sudo apt-get install aircrack-ng</span>
Without this you must use the command:
<span onmouseover="_tipon(this)" onmouseout="_tipoff()"><span class="google-src-text" style="direction: ltr; text-align: left;">sudo airodump-ng start nome_scheda</span> sudo airodump-ng start nome_scheda</span>
With it will launch the service to scan WiFi networks that might be launched with:
<span onmouseover="_tipon(this)" onmouseout="_tipoff()"><span class="google-src-text" style="direction: ltr; text-align: left;">sudo airodump-ng nome_scheda</span> sudo airodump-ng nome_scheda</span>
At the end of the scan received a list of available networks.