What kind of sensors could I use to determine the exact location on a flight of stairs, a person is?
It’s a wood staircase, one side to the wall. One side not. Approx 36" wide and will have a runner strip of carpet up the middle so could hide pressure mats.
One mild issue is we sometimes have stuff in the steps so a ‘beam’ might not work. Plus I’d like to not flood the stairs with ir.
Not fussed about daylight working, but dark is a must
Depends a bit on your knowledge about structural dynamics. You could use acceleration sensors and analyze the modal response of the impact by stepping on a stair. But nothing done in some days.
Simplier would be a sensor that measures distance of an object.
Btw what are you planing, self shooting guns? 
Not quite as glamourous as guns lol
I want to use a strip of neopixels (copies) to light up the step youre on in one colour and then the one before and after in something else. 100000% pointless, but awesome nerding 
We are redecorating the hallway and stairs, so with all the trim removed its ideal to hide wires etc
I dont think that there will be a out of the box solution.
I would prefer distance measurment or the pressure mats
When I read this I was in the middle of playing around with an ultrasonic sensor (that is capable of measuring distance) connected to an Arduino.
This got me thinking; what about one of these in the side of each step? Naturally you would have to select the side where you are least likely to “have stuff” if possible.
If you define your “open distance” a bit beyond where you think a person will naturally be located in the step when walking up or down, and stay away from that area when you place “stuff”, it should be possible to have this work even if you now and again place something in one of the steps.
Would ultrasonic sensors be ok close to each other as in steps, and how annoyed will the cats be? Lol
Might need to do it with pressure mats under the new carpet 
I’d say you need a distance sensor on the side of each step… Would have to just build logic in so that if you leave something on a step it may light up for a little while but then it would automatically cancel it out because the object hasn’t moved in a certain timeframe…
I’ve been playing longtime with the idea of having a stair-controlled wall lighting, too. I agree, 100000% nerding, but hey, just for the fun of it. To be honest, I never made it. But I’ve spent quite some time on evaluating technical possibilities.
There’s ultrasonic (distance) sensors with a board to deliver binary output for about $2 on *bay.
But he most interesting one I came across was to basically have - just two parallel wires per stair and to use induction.
I’m afraid I don’t find the article any more, but the author claims that a person crossing the wire results in enough inductive load to be able to measure it as current on an analog sensor. The great thing is simplicity and invisibility. Easy to deploy one or even more wires per stair. If you happen to have an analog sensor, give it a try.
When I was a kid (waayy back in the 70’s), I built a sensor from aluminium foil under the carpet in the top stair of our staircase, which picked up the 50hz once someone stepped on it, to sense when someone approched my room. I remember it worked quite ok, before my mom told me she did not want the battery case and cables (I was only about 12yo, so I guess it was not very pretty…).
Benfit of that early construction of mine, was that it was easy to fit, and had I been older, it would probably been more nicely fitted.
I had a self built wooden control panel by my bed with red LED’s (which where quite new by then) and switches for the sound system hidden mostly under my bed, except the speakers. I still remember getting shocks from the transformer, which where just laying in the dust under my bed. (220V at the time). Still alive though…