I wasn't sure if it can be configured to prohibit key access. How strong is it? If it can, it's unauthorized. If it can't, it's not keeping your landlord out.

He said he wanted to know when the landlord came, not keep him out. As far as I know, it won't even attempt to stop the key from opening the lock, but it will detect it.

If you keep your landlord out, you're violating your lease. At least under any sane lease.