A signal-carrying member responsive to the presence of a solvent and suitable for use in a security cable or a liquid leakage detector, comprises a conductive ink 20, consisting of a particulate conductive material and a non-conductive carrier medium, printed on to a non-conductive strip 17 and conductors 16 such that when the printed material is contacted by a solvent to which the carrier medium is sensitive, conductive material will be released from the printed material and can be used to vary a signal passed through the signal-carrying member.