Macintosh:

The Airport Control Strip in the bottom left corner of your screen will have lit green dots indicating the strength of the connection. If there are no lit green dots, then you are out of range.


Windows:

There will be a connection icon in the System tray:
If you see green bars, you are connected and have good performance.

If you see yellow bars, you are connected, but may have slower performance. If you want better performance, you can move to another location

If you see one red bar, you have no connection at all and will need to move to another location to connect.