how does a long range infrared proximity sensor work?

Generally speaking, making an infrared receiver more sensitive is just a matter of installing a better preamplifier after the sensor. If you really wish to, you might use a lens that is transparent to infrared to concentrate more of the signal on the sensor (I’m not sure where you’d get them; ordinary glass lenses are not very transparent to infrared.) Or, try putting the sensor at the focus of a small parabolic reflector; you could take one out of an old flashlight. I’m speaking in terms of building it yourself; I don’t know of any commercial products. If you have no electronics technical skills, try asking an outdoor security alarm company, they might have the sort of equipment you want but I’ll bet it would be expensive. Good luck anyway.

24 JAN 07, 0207 hrs, GMT