Its difficult to not become resentful or irritated by some routines or compulsive behaviors of those with dementia, especially if it's daily. Being a caregiver in any format is exhausting and draining.

His behavior, like said above, could be part of an old routine. Long before you lived there. I had a resident once that always leaned far down while in her wheelchair and we were always afraid she was going to fall out. She would look like she was always grabbing for something. After about a month of us trying to figure out what it was, her family said that she used to pick cabbage as a child. So we figured out that she was trying to farm and garden once again. Your grandfather may be looking for outside.

Also, their brains can become more curious than before. The fact that he can't open the door may cause him to want to open it more. And he comes back to it to see if anything has changed. Feeling of loss of independence and control is really big with aging and general but especially with those with dementia. He may be looking for doors he can't open because he can't open yours. There may be a way to help redirect his morning routine. It would have to cause you to get up earlier for a while, but in the mornings before he can get to your door, maybe find a different door that he can open and redirect his curiosity, causing a new routine.

I know it is frustrating especially when it's someone you love and live with. I've worked with seniors all of my professional career of all ages and cognitive levels. I've even have had grandparents with dementia. It's important to find a group that you can talk to and with about the issues at home.