many thanks for these replies, looks like i have plenty to learn yet....
i dont think that the angle that the sensors read will be much of a problem if they overlap, it may be interesting to have two sensors detect the same person and respond accordingly.
sorry for my lack of knowledge but can i ask if the infra red and/or the gp2d12 sensor detects over a horizontal plane or in a kind of funnel 3d shape? i would like to have some of them above each other. hope this makes sense
i think my next/first step will be to get an arduino and one sensor and learn from there
many thanks