A new electrochemical system is capable of controlling an integrated analog or digital display and modifying the load resistance of an RAID transponder. In contrast to conventional smart labels the self-writing system is active even when no power is supplied by a reader. The self-writing mechanism and the display functions are based on doping front migration (DFM), an electrochemical effect occurring in structures composed of intrinsically conductive polymers and described here for the first time. This ultralow-cost system represents a new class of smart labels containing analog and digital functions and capable of displaying changing information to the human eye. The device may also be used as a time-temperature integrator that monitors and reports product storage conditions. This may be very useful as a "best before" label on food products. (c) 2008 Elsevier Ltd. All rights reserved.