Does Wake Up have its own CCTV? I'm wondering if the reason the key card wasn't used was because the door was open (either left by accident, another person he was sharing with-if he was sharing--opened it)..
It seems he was intending to head home, and sent messages long after he'd be expected home (perhaps he got home, sent the messages, possibly slept for a bit... Got up and made the bed and then headed back out for sunrise)... Perhaps with someone who had transport (meaning no Cctv of him walking anywhere) or perhaps along the beach.
Is the beach particularly rocky? To the point that someone could slip and bump their head, then be taken by the tide? Does the high tide cut off access along the beach - which might mean someone already on the beach might try to pass between waves/through water that was initially shallow, and then got knocked over by a wave and dragged out by the current before dawn... Assuming the phone was waterproof as someone suggested earlier, perhaps henwas taken by the currents around the direction of the lighthouse and it took time for the phone to become waterlogged enough to lose power and cease working.
Is anyone familiar with determining then water current on particular days? Or is anyone familiar with that beach?