Luke had been chatting with Jude and several others, not thinking much about the security and metal detectors positioned at the entrance. After all, he was familiar with those muggle devices, the muggle world being his own and he knew all the students would have to walk through it just like his primary school field trips had done in the past. When he had passed through and waited on the other side for his friends to join him, he noticed Theo being taken to the side. Ordinarily, he would have piped in a joke about her hiding illegal weapons but he knew how strict the muggle security officers were, and decided to hold his joking for after their search.
He merely grinned at Theo when she called out, and stepped over closer just in case she needed a hand. He figured he was probably in a better position to do so, being muggleborn, than her other friends. "At least you don't have a laptop," he replied to her. "Those they swab." He waggled his eyebrows.