Elliot's house may be locked for a variety of reasons. It could be that someone inside the house is in danger and needs to stay safe, or it could be for security purposes; Elliot may not have wanted anyone to enter his home without his permission. Another possibility is that Elliot has been away from home and needed to secure the property while he was gone. Regardless of the reason why, it's clear that Elliot had a valid purpose for locking up his house.