HI Kristian, I fitted one called an 'occupancy sw.' to our bath room in place of the pull sw. because of 'kids' always leaving light on! Kids now 23 & 30 & long since left home, I still like it but 'der Boss lady' hates it as if she lays in tub too long reading etc light goes off, followed by frantic arm waving Ho! Ho! Ho!
Electrically need a neutral not normally at sw. so twin/E from light must be changed for 3 core /E