How to switch off m10 sc

Hello, I just bought an m10 sc (with the m110 sc bundle) and realised I cannot find a way to switch off the m10 sc handset. I tried to long press on the red button ( off ) - and of course I read the manual itself -, but it doesn't seem to work. I don't know if it set like this (no option to switch it off) or there is a problem with my device in particular. Thank you in advance.