One option might be to have the sniffing device setup with a hidden wireless network (of some sort).

Then when you walk around, sit in the food court eating, or if the device is close to the outside, sit somewhere out of sight of the cameras with a strong wifi antennae and grab whatever data.

Unless they have some "free" wifi that the device could hop on to send it to some server somewhere.

Using that and / or 4g would make it easier to find the device and, of course, the person though.