We had this snake in our bungalow on Koh Lanta, Thailand. From the reaction of the employees at the resort I can tell that it is venomous, but that's all I know. I am curious, does anybody know what species it is?
If the resort is near a water body then it is highly likely that it is a keelback snake.
For determining whether it is poisonous or not it is extremely important to look at the scale pattern on its ventral side(belly). Unfortunately that is not visible here.