Abstract: The inertia switch device (1) comprises an inertia mass (6) which is movable from a rest position when the device is subjected to an applied acceleration or deceleration in a horizontal plane, a first electrical contact (5) movable between a first stable position in which it engages a second electrical contact (3) and a second stable position in which it no longer engages the second electrical contact, and support means (4) having a bifurcated portion (24) for carrying a bifurcated portion of the first electrical contact (5). An operating means (27) is struck by the inertia mass (6), when the applied acceleration or deceleration exceeds a threshold value and moves the first electrical contact (5) from the first to the second stable position. The operating means (27) has a first limb (31) which is struck by the inertia mass and a second limb (28) with a bifurcated portion which is pivotally mounted on the support means.

Abstract: Radiation detection apparatus is disclosed including a first detector (6) for detecting radiation at a wavelength which is preferably in the infra-red region, and a device for sensing the presence of an obturating element (11), which element acts to prevent operation of the first detector. The sensing means includes a transmitter (14) which transmits a signal at a second wavelength, and a second detector (15) responsive to and arranged to receive the signal in the presence of the obturating element, preferably by reflection of the signal from the element. An alarm (10) may be activated in response to detection of radiation or of the transmitted signal.