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The development of intelligent materials that can respond to the application of an external stimulus is of major interest for the fabrication of artificial sensing devices able to sense and transmit information about the physical, chemical and/or biological changes produced in our environment.[1, 2] In addition, if these materials can be deposited or integrated on flexible and transparent substrates and processed employing low-cost techniques their appeal is greatly increased.[3, 4] In this context, organic materials, which have already shown a huge potential in a wide range of (opto) electronic applications, can play a crucial role.[5–7] Here, we show that by using bilayer (BL) films, composed of a polymeric matrix with a toplayer formed by a crystalline network of a conducting molecular charge-transfer salt, it is possible to translate micrometer-scale elastic elongations of the film into reversible deformations of the soft organic charge-transfer salt crystals at the nanometer scale. These multiple-length-scale movements are responsible for the ultrasensitive piezoresistive properties of the BL films that are extremely sensitive to strain changes with durable, fast, and completely reversible responses.[8] Such BL films have a sensitivity that is one order of magnitude larger than the most commonly used electromechanical sensors.[9] In addition, a few proof-of-concept experiments with simple prototypes are also reported demonstrating that these flexible, low-weight, transparent and soft composites are very attractive as a new generation of durable and low-cost all-organic strain sensors, being highly promising for a wide range of applications in areas such as …