A novel system for the detection of ammonia was developed by monitoring the conductance of inkjet printed or screen printed polyaniline films with a radio frequency detector. The system has the advantage of non-contact detection of ammonia within sealed packages. Since the sensor is a passive printed film that is externally interrogated, it does not require an internal power source or associated circuitry, and therefore may be a low-cost device suitable for smart packaging applications. When printed on a suitable substrate, the sensor can be cycled several times using heat or a volatile acid to regenerate the polyaniline surface. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.