Answer:
No...
Step-by-step explanation:
I think this may be a trick question... so from my reasonable logic, I'm gonna say no because more often then not they are attached to the wall with nails/screws. Or they are hanging.
So they could come off. Also if someone was desperate, they could always grab a chainsaw and force it off of the wall. Not a great idea though, then the wall would be broken!! Most likely the clock too!