Abstract: A liquid precursor for a gel comprises liquid polyethylene glycol (PEG), a gelling component such as a mixture of acrylic derivatives and optionally a polymerization initiator. A suitable polymerization initiator is the photoinitiator diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide. Gelation may be achieved by irradiation with UV. The resulting gel may be free from water and exhibits high viscosity over a wide range of operating conditions. The gel is suitable for use in an indication device suitable for indicating exposure to an accelerating force above a desired threshold. The indication device may be used to indicate whether an information carrier (such as a computer-readable optical disc) has previously been accessed.

Abstract: A compact disc (10) for a computer incorporates a security device for preventing non-authorized reading of data carried by the disc. The security device includes an LCD laser blocker (16) which is activated or deactivated by means of a microchip (13) powered by a cell (14) and/or solar panel (15). Authorized reading of the data is possible by a fingerprint scanner (12) linked to the microchip and causing it to deactivate the blocker (16), when the scanner recognizes a user's fingerprint which the microchip matches to a programmed authorized fingerprint. Also disclosed is a data carrying compact disc (20) which incorporates security means to allow a first reading of the data of the disc, but to prevent such reading thereafter. An area (21) of the disc, such as a FAT file, can be arranged to be destroyed or blocked, to prevent subsequent reading thereof by the disc reading means.

Abstract: A disc or like article (10, 115, 119) rotatable by drive means, such as a compact disc for use with a computer, includes indication means (12, 110, 120) which, when the disc is rotated at or above a predetermined angular velocity, provide an indication that rotation has occurred, which indication can be important if the disc contains confidential information. The indication device can be a tube formed with two enclosures separated by a breakable membrane (15, 16, 112, 122), a colored liquid/gel (17, 111 121) being in one enclosure and passing into the second enclosure, by breaking the membrane, when the disc is spun, thereby providing a visual indication thereafter of the spinning having occurred The invention also relates to such an indication means, per se, for after-fitting to a disc recorded on by spinning, and to a method of producing a disc with said indication means.