zeez writes:
I was wondering about that. Let's say a land lord wants to spy on
their tenants and make their lives miserable by coming into their home
everyday. ...

Google for "quiet enjoyment" (with the quotes). Quoting from
the first match:

"Quiet enjoyment is a right to the undisturbed use and
enjoyment of real property by a tenant or landowner...

"Courts read a covenant of quiet enjoyment between the
landlord and tenant into every rental agreement, or tenancy.
Thus a renter, or tenant, has the right to quiet enjoyment of
the leased premises regardless of whether the rental
agreement contains such a covenant."

In other words, it's common law, so everyone here who has told
you to consult the laws for your state or the terms of your
lease is wrong.

Any housing court judge with a modicum of common sense would
consider frequent intrusions by the landlord into an apartment
to be a deprivation of the tenant's right to quiet enjoyment,
if not ipso facto, then certainly after the tenant has asked
the landlord to stop. It would be recognized for what it is
-- an attempt by the landlord to harass or spy on the tenant,
for whatever reason.

So yes, the victim of such intrusions, if s/he were so
motivated to do so, could file a complaint in housing court
and ask the court to award damages for breach of contract and
injunctive relief (i.e., an order barring the landlord from
continuing to intrude unnecessarily into the apartment).

Usually, state law prohibits retribution by a landlord against
a tenant for filing such a complaint, but there are ways
landlords can get back at tenants which are very difficult to
prove in court, so if a tenant decides to go this route,
s/he's almost certainly asking for some grief at the hands of
the landlord. It is therefore not a step to be taken lightly.