Is it normal for motion sensor lamp in stairwell to turn on when im in apartment

They recently installed motion sensing lamps in the stairwell of the apartment building where I live and we've noticed that everytime one of us in the apartment walks towards the front door we see through the peephole that the lamp out in the stairwell turns on. How is it possible that the lamp can sense movement from inside our apartment through the front door? When I walk through the stairwell to get outside I have to be right next to a lamp for it to turn on so how does it make sense that the one on our floor turns on when someone walks near the front door inside the apartment?

Is It Normal?
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  • Most of those lamps have infrared sensors - basically heat-detectors. When it senses the presence of something warmer than the surrounding background temperature in its field of view, it turns on.

    If the front door of your apartment was extremely flimsy, I suppose the lamp could detect the heat of a body behind it, but the door would have to be almost literally paper-thin, and the fire codes in most places mean apartment doors need to be a lot more robust than that. And the detector would also need to be very sensitive, which it seems it isn't, from what you say.

    Another possibility is that the lamp is being constantly triggered by air currents in the stairwell, and it's just coincidental that you've seen it turn on when looking through the peephole.

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    • No it definietely senses when someone walks towards the front door. We've tried it in my family by standing in the hallway looking at the door (the peephole isnt covered so you dont need to look through it, you just see how it goes from being dark to lighting up when the light goes on outside) and nothing happens. Then one of us walks towards the door and it lights up outside. Its really weird because yeah the front door is robust.

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      • I suspect I may have figured this out. I've never heard of them before, but microwave sensors for security lights do exist. The one I link to below claims to be able to penetrate wooden doors and thin walls.

        https://www.amazon.co.uk/degree-Microwave-Motion-Detector-220V-240V/dp/B07BCCXQJZ/ref=pd_lpo_60_t_0/261-3984002-2136006?_encoding=UTF8&pd_rd_i=B07BCCXQJZ&pd_rd_r=89866b77-66c3-4692-99c0-bffe85ad1b9a&pd_rd_w=hKDje&pd_rd_wg=vgoBS&pf_rd_p=7b8e3b03-1439-4489-abd4-4a138cf4eca6&pf_rd_r=T4DJ5A56Z2773AT0K1FM&psc=1&refRID=T4DJ5A56Z2773AT0K1FM

        If you now say that your apartment door is metal, I really have no idea how what's happening is possible.

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