Here’s an interesting device that can log all the data off a wifi network. Of course, you can probably use a PC to do the same thing but this one is portable and can act as a spy’s tool. I bet FBI and CIA are already using something like this.
This could be a great way to track down if your wife’s cheating on you. Of course, let’s not hope you are at that point ever.
This Instructable shows how to make a datalogger from an Arduino and datalogger shield connected to a TelosB wireless sensor board and a battery that is large, but not wheelbarrow large. Your data goes onto a SD memory card on the datalogger for pickup later (whenever you have to change the batteries on all the wireless radios in your network, for example).