Evan Schuman's StorefrontBacktalk

Just when you thought you had figured out how to deploy in-store mobile devices, something comes along to remind you that it’s not that simple. Last month, the FCC ordered 20 small online retailers to stop selling illegal devices that jam the signals for mobile phones, GPS and Wi-Fi. No surprise there—but also not much impact, because such devices are easily available from other online retailers. That means anyone willing to pay as little as $80 could walk into a store in your chain and jam the Wi-Fi that your mobile POS depends on.

It’s a classic single-point-of-failure problem, and it could be frighteningly disruptive—especially since this holiday season will be the first at many stores with lots of in-store mobile devices in use, and almost all retailers are using Wi-Fi to keep them connected. A saboteur who uses a pocket-size jammer wouldn’t have access to payment-card information, but what’s supposed to be an impressive demonstration of retail technology would just irritate customers and frustrate associates—especially during the high-volume times that mobile POS should be a relief. And that’s just from an intentional saboteur. Unintentional Wi-Fi jamming could have even worse effects.

The problem is that many in-store mobile devices, including the iPod Touch, use Wi-Fi with 2.4 GHz signals. That frequency range is not exclusively for wireless networking. Cordless phones, wireless microphones and other personal radio products were made for years that used signals in the same range.

That means a saboteur or prankster isn’t the only one who might walk into the store and jam the Wi-Fi. To be clear, what’s illegal is to “willfully or maliciously interfere with or cause interference to any [legal] radio communications,” as the FCC’s order put it. It’s also illegal to market devices for the purpose of creating interference. So that saboteur who turns on a jammer in the store is breaking the law.

But a shopping-mall musical performer who comes into the store and forgets to turn off her wireless mike—that’s not illegal. The mike’s not illegal, and neither is forgetting to turn it off. That doesn’t make it any less a problem if it disrupts a customer’s mobile checkout.

Small children who bring in certain radio-powered toys can be just as disruptive, even if the kids themselves are well behaved. Just as bad can be malfunctioning phones or PDAs that scatter static across the Wi-Fi band, especially if it happens in momentary bursts that are just long enough to break a Wi-Fi signal.

Even more of a potential problem is Wi-Fi equipment from other retailers—such as pop-up stores.