Abstract: A personal computer (2) is responsive to the presence of an authorised user to transmit release signals from a CPU 22 to a CPU 28 to cause the CPU 28 to effect the release of a locking mechanism (34) controlling access to drawers of a desk or filing cabinet for example. In the absence of periodic refresher signals from the PC 2, the CPU 28 causes the locking mechanism to lock the drawers to prevent unauthorized access. The transmitted signals from the PC 2 may also be used to prevent or allow use of electrical or electronic apparatuses and/or to control environmental conditions appropriate to the presence or absence of users.

Abstract: Apparatus for an interactive video system comprising a transmissive projection screen (8) from which an image projected on to the rear surface is visible from the front side but not visible from the rear side, a projector (20) to project display images on to the rear surface of the screen (8); and a video camera (22) positioned to video a user (2) in front of the screen (8). The user (2) effects a writing action on the screen (8) using a dry pen (24) comprising infrared LEDs (64) which operate when the dry pen (24) is pressed against the screen (8). These emissions are detected and position decoded, and a corresponding image projected on the screen (8) so it appears as direct writing to the user (2). The videoed image of the user and the input written data may be combined and transmitted during a videoconference to corresponding apparatus used by a further user (4) who thereby sees interaction between the first user (2) and the written data.