If you start your own gym, would it be legal to have oneway mirrors in the locker-room to your office so you personaly can make sure no theft happens?

Or would you be obligated to inform your customers about this extra security? Would prefer to not warn potential thiefs.
If you start your own gym, would it be legal to have oneway mirrors in the locker-room to your office so you personaly can make sure no theft happens?
Post Opinion