We have a council offices & the window is like an alloy sash window. If the central lock is not on these windows slide up slightly, so there,s a small gap at bottom & it is realy difficult to see, i have others that are no problem in dark, new build etc.
Its just a case of knowing what to look for & preparing for what could go wrong.
The above office some windows slide open as you clean them aswell, so you realy have to be careful.
Gary