@Johan **************
Every foreigner has to be reported in the TM30 system of Thai Immigration within 24 hours after arrival at an accommodation.
The reporting can be done online or in person and is called TM30 registration.
Your hotel, your landlord, your friend, your guesthouse or your resort are by law required to report a foreigner within 24 hours of arrival at the accommodation.
Immigrations have begun to enforce the TM30 a few years ago. On many Immigration offices, you will be refused any service unless your TM30 isn't up to date