What is he searching for him to check his backdoor so much

I Think he wanted to check if he has any gadget to make him invisible

Spoiler
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In the past TL Jaechan and the Director Yoon i.e., Woojin's stepmom whom he wants to frame for the bomb were in cahoots in a way. Now Jaechan understands that she wasn't simply helping him get with Woojin, but using him to try and control Woojin or make his life difficult. But Woojin still thinks Jaechan and director Yoon are close and is afraid he'll inform her of his plan to frame her for the bombs so he is searching for potential communication devices.