For the past few weeks I have been over-engineering the replacements for the security lights outside the front of my house. They are now screwed into reclaimed teak pads which should have a service life of 80 years. The cable is armoured and secured to stainless steel bases. The PIR sensors are wired together so that either sensor will light both lamps.
The most interesting bit is the infra-red mirror in front of one of the motion sensors. The sensors have a wide field of view, but it's not quite 180 degrees. What this means is that when you approach my front door the lights will come on, but when you leave the house, you're in the sensor's blind spot and you're left in darkness until after you've tripped down the stairs.
The sensors work on infra-red emitted by warm objects. Polished aluminium will reflect infra-red radiation. I just happen to have some aluminium foil tape from another project, but the shiny side of kitchen foil should work just as well. I've put a little plate covered in foil tape in front of the sensor at 45 degrees. Instead of looking out the front, some of its field of vision is now pointing directly at the front door. The most amazing things are that 1) it works perfectly. 2) I managed to get it working without a thermal camera, so I couldn't see what it could see, or whether the tape was actually reflective in the infra-red.
Richard "Let There Be Light On The Stairs" B
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