How to place down a Motion Detector?

[MinishiNiseru]

I have looked all over trying to find out how to place / build / install items on the sub.

[Mr.America]

Have it in your inventory, double click on it or press the associatied slot number to equip it, aim with mouse, place with left click.

Alternative, use sub editor.

Use wrench to detach it from the wall again.

Items can only be placed on background elements, e.g. there needs to be a wall there, you cannot place it on water.

[MinishiNiseru]

Awesome! Thank you very much.