Case law
You may find this excerpt from the following link helpful in seeing through all the psychological intimidation at play:
Landlord/Tenant Supplement Pt.1
Absent express language in the lease to the contrary, the law implies a promise by the landlord that the tenant will have peaceful, quiet enjoyment and use of the premises through the term of the lease, HYM Restaurants, Inc. v. Goldman Sachs & Co., 797 S.W.2d 326 (Tex. App. -- Houston [14th Dist.] 1990, writ denied), and that the premises will be exclusively for the use of the tenant.
A breach of the tenant's right to the exclusive use of the premises is called a trespass (and, if material, it entitles the tenant to terminate the lease). The tenant may also recover damages caused by the trespass. Clark v. Sumner, 559 S.W.2d 914 (Tex. Civ. App.--Waco 1977, no writ)(landlord allowed dog to enter tenant's dwelling which violated covenant).
Another action that should be considered is an action for forcible entry. But the right to exclusive use can be partially waived in the lease to allow the landlord reasonable entries without being in violation of the covenant. See HYM Restaurants, 797 S.W.2d 326.
Many landlords ignore the basic tenant right of exclusive use and quiet enjoyment, and enter the apartment at will without even knocking first. Unfortunately, the tenant has the right to terminate for only the most severe and permanent violations.
The tenant may request that the landlord install a keyless deadbolt on any door, at the tenant's expense, which will at least prevent any entries while the tenant is at home.
Tex. Prop. Code SS 92.157.
Another legal remedy that may be available to discourage the landlord and compensate the tenant for improper entries is the tort of invasion of privacy. Prosser has determined there are four categories contained within the tort, including "an intrusion upon the plaintiff's seclusion or solitude, or into his private affairs." W. Prosser, Handbook of the Law of Tom SS 117 (4th ed. 1971); Gonzales v. Southwestern Bell Tel. Co., 555 S.W.2d 219, 221 (Tex. Civ. App. --Corpus Christi 1977, no writ).
The Texas Supreme Court announced in Billings v. Atkinson, 489 S.W.2d 858, 859 (Tex. 1973), that every citizen has a right of privacy defined as "the right to be left alone, [and] to live a life of seclusion ... " There is no indication that the Court intended to excuse landlords from respecting the right to privacy held by tenants. The Court also noted that proof of actual damages in not necessary to a recovery. "Damages for mental suffering are recoverable without the necessity of showing actual physical injury in a case of willful invasion of the right of privacy because the injury is essentially mental and subjective, not actual harm done to the plaintiff's body." 489S.W.2d at 859.
Finally, severe intrusions by the landlord could also constitute a deceptive trade practice actionable under the DTPA. Tex. Bus. & Corn. Code SS 17.41, et seq.
Landlords have a right to inspect their property periodically and at reasonable times, or to make routine or requested repairs on the dwelling during reasonable times (especially if advance notice is given). The key word is reasonable. These entries must be reasonable and must not interfere with a tenant's right of privacy and enjoyment of the premises.