New in-store ad device

This article in Ad Age describes a new product that will play ads when somebody walks by. The technology sounds really cool ("The small devices cost just $300 to manufacture, are battery operated, attachable to store shelves and operated by a remote server the size of a cigar box") but I wonder about one of the supposed benefits.

The article says that the new system is intended, among other things, to overcome objections to in-store systems that run constantly. But most stores that I'm in have multiple customers in every aisle at least in bust time periods -- so won't it be running almost constantly? I also wonder about the sound bleeding over from one device to the next, assuming that stores will have several of these devices.

But I guess that's the sort of thing that gets ironed out in the test. The big question will be competition from the stores' own in-store networks.