The present invention relates generally to signal processing and cell phones. One claim recites a method comprising: receiving a signal from a cell phone; determining, based at least in part on the signal, whether the cell phone is physically located in a predetermined home area; and if not in the predetermined home area, communicating a machine-readable code detector to the cell phone for use as its primary machine-readable code detector to detect machine-readable code while outside of its predetermined home area. Of course, other claims are provided too.