I could just use one or two wall mounted motion sensors which would cover the whole lobby, but i want something more fancy. "Laser trap"-sensor would be cool but i didn't want to have a transmitter and a receiver on every door or doorway. I'm planning to use Ultrasonic sensor so that the transmitter and receiver are in the same location.

I measured and calculated the amount of doorways and floor trim i would light up and set sensors for. Floor trim amount is about 6,71 meters and doorways 8 pcs. For the lighting I will use WS2812B based RGB led strip so i can get a cool lightup-effect depending on which direction a person enters the lobby. 6,71 meters of 60 leds/meter led strip would need around 120W of power so I think i'll stick with the 30 leds/meter led strip.

I need to order the parts so i can get to testing.