TM 30 - Thailand's Immigration Form for Notification of Reisdence of Expats
The TM 30 form is an immigration requirement that applies to expats living in Thailand and house or hotel owners with expats living on their property, to notify the Immigration department of the residence of non-Thai nationals within 24 hours of arrival.
The law has existed in Thailand in the Immigration Act since 1979 but only recently been enforced to include residential premises. Failure to notify the immigration department can affect visa extension of the foreigner concerned and impose penalty on the landlord.
The International Legal Counsellors of Thailand share more details on the TM 30 and the offline and online notification process here.