Can the landlord search my room in Thailand?
No the landlord can not search your room, house, apartment or Office. Even if they say that on a notice we got from one of our blog readers. You are off course responsible for whats going on in your rented apartment and the landlord has no right what so ever to go in with the key or go inside by force.
The right he has should be stated in the contract like if he needs to check the water pipe or wires for power he can ask permission to come and see you. But he has to do so when you are home and he have to tell you a few days in advance he can not come just when he feel like it.
If you feel that your landlord has stepped over your rights please report to the police or call them if he tries to enter the room while you there. If the landlord has brought the police with him you do not need to let them in before you have a lawyer or witness that you trust.