The invention relates to a semi-conductor transducer, and to the use thereof in an electron donor or electron acceptor space sensor. The center member includes three perimeter assemblies that each cooperate with a corresponding leg member. Alternatively, the mounting panel may be engaged directly in a C-channel carried by a front lip on the merchandise display shelf or the front of a label holder having sign-receiving channels defined on the front face of its cover member. The encryption acceleration data and encryption initialization data reduce a number of calculations needed on the second device to initialize and use the private-key encryption method, thereby reducing the overall time needed to create a cryptographically secure communications channel between the first device and the second device. Preferably, the activating system also includes a user operated reset button and a shutoff circuit to allow the user to stop transmission of the signal by the signal emitter. At least one first watermark indicator is generated based on the the watermarked original signal and the watermark and at least one second watermark indicator is generated based on the suspect signal and the watermark.