Starting in 2015 it was a requirement for a buyer of a SIM card to register the purchase using his or her personal details. This has now moved on and as of 1st February, 2018 they want bio-metric data as well. At first this was only going to apply to Thai nationals buying a SIM, but it appears it will be applied to foreigners as well.
The biometric data could be a fingerprint scan, facial scan or an e passport scan. It just depends on what equipment the seller of the SIM card has installed and can actually use. I am sure there will be a lot of problems!
Authorities state that this is for the benefit of National Security and no other reason.
We will see what happens. But be prepared after the 1st February, 2018 if you go out to buy a DTAC, AIS or True SIM Card, even in 7 - Eleven.