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Also seen in large rooms, such as a gymnasium or an auditorium, are devices to detect a projected beam. A unit on the wall sends out a beam, which is either received by a receiver or reflected back via a mirror. When the beam is less visible to the "eye" of the sensor, it sends an alarm signal to the fire alarm control panel
Optical smoke detector ?
I would place it 8 foot up the wall (to stop idiots putting chewing gum on it).
Quote from: imatfaal on 20/08/2010 16:56:53I would place it 8 foot up the wall (to stop idiots putting chewing gum on it). Cold smoke will run along the floor, so putting the sensors/reflectors 8 feet up would reduce their usefulness.
Being near floor level really rules out smoke detectors
some of them seem to have a paired device in the ceiling
Quote from: imatfaal on 20/08/2010 14:04:28some of them seem to have a paired device in the ceilingso the beam would cover from ceiling to floor.
I have noticed these strange devices on some London Underground Platforms for a few years now. Not all have them - but the Jubilee Line (one of the more modern lines) has examples at most stations that I use.Its is obviously some form of optical device - and some of them seem to have a paired device in the ceiling, but by no means all of them (or you just can't spot it). Other info- They do not move, although the paired devices seem to- Actual size is about 12-13 cms cube with 5 cm cylindrical bit- they are about 12-18 inches off the floor and attached to the wall- the orange glow is real not a photo-artifact- there seem to be optics inside - but I have never looked straight in (I like my retinas as they are)