Yes, but there's several problems with these - the majority are radio controlled clocks which don't work inside our heavily insulated building so are next to useless. Normal wall clocks would be OK but they are hard to keep synchronised between 40 classrooms, just like staff's watches. We just need a definitive signal to everyone that the lesson is to end as it can be difficult if one teacher lets pupils leave even a minute before others as then children are outside teaching areas while another teacher is still packing up etc etc. Similarly if a staff member forgets for whatever reason to look at the clock, the automated message/sound would be a reminder.
Hope that explains more!