Try installing a shield which blocks it from anyone passing by but triggers when someone steps on that top tread.

 

It depends on the construction of the stairway but if there is vertical wall surface above the first step, you can position it there and it can't "see" the hallway. Of course getting a wire there will be a treat. You'll also want a fast acting sensor. I hate it when they are slow and you have to take a couple steps in the dark and trust it will come on, or stand still a second for the light to come on.

If you want a whole science fair project you can run a beam-break sensor across the first step that operates a relay that switches the light. These are not just mission impossible gadgets, they are used for alarm systems and other applications and they are not real expensive. These can be made very small and inobtrusive, and they are dead reliable.

There are industrial safety beam breaks and light curtains but you don't want all that.

 

If you want a whole science fair project you can run a beam-break sensor across the first step that operates a relay that switches the light. These are not just mission impossible gadgets, they are used for alarm systems and other applications and they are not real expensive. These can be made very small and inobtrusive, and they are dead reliable.

I would put it just in front of the first step if possible. A step or two onto a dark stairway puts you right in the middle of the liability zone.

For that matter, how much savings would be realized on a stairway anyway? I have refused to put motion sensors in areas where a failure or an early timeout because someone sits still long enough would endanger personnel. Not worth the hassle.

 

What kind of lights are in the stairwell? They make sensors which attach right to the light fixture.

 

I have floodlights mounted Highup in the trees over my driveway, in three different spots, and then on the corner of the house by the garage. They are all controlled by three separate motion sensors.

The one closest to the street I mounted behind a tree so that it could not “see“ anything between it and the street… It can only “see“ a warm object that is actually pulling into the driveway.

What you need is to duplicate this, an actual physical obstruction to the site line of the motion sensor you’re using relative to its placement. There is no other dependable way around this that I can see…

I remember motion sensor floodlight kits which came with stickers to Obscura portions of the motion sensor that you did not want it to sense motion. But I don’t think that is as solid a solution .

In New York City‘s new police Academy headquarters in college point queens the building was to have LEEDS certification, so the stairwell lighting requirements clashed with New York City code in that egress stairwells must remain light and 24 hours a day seven days a week.

So what they did was install permanent lighting constantly lit, as well as additional lighting activated by motion sensors. But the ironic thing is that the permanent lighting 24 seven was more than adequate to light the stairwell and the entire additional motion sensor system was simply redundant and unnecessary.

But it did however increase bid costs, and therefore padded the bill for the designer. So there’s that.