Well, I wouldn't want my credit card numbers stole from Wi-Fi devices...
The Best Buy cash registers used a Wi-Fi network, which uses a standard known as 802.11b. It runs on three channels in the unregulated 2.4GHZ spectrum, which is also used by cordless phones, microwave ovens and many Bluetooth products. Because the information is transmitted through the air, a person can "capture" the information from the parking lot outside the store or anywhere within about 300 feet of the source. - CNET