Boundary sensing

[Maru]

can you guys give me some suggestions on what type of sensors can i used to detect the existence or motion of an object once it pass through certain threshold of a boundary? I would like to create some kind of a room with transparent wall (the sensor range). I've depicted a drawing of a man in a transparent room as above.

[nagelc]

Kind of old school, but you could use a laser, some mirrors and a detector. It would only work if they broke the beam however.

You might be able to use regular PIR motion sensors and cover part of the lens. Or possibly make a custom lens that sees a vertical slit . . ...

I just tried it on one of my PIR motion sensors. Black indelible ink did not work -- IR just goes right through. making a vertical slit by taping off with duct tape sort of worked. The width of the detection area spread out pretty fast, but it seems like it could work if you don't need too much precision. There might even be lenses for that purpose.

[Maru]

I've thought of that already but @nagelc thanks for the suggestion though!!