When I'm home alone? Well, there are certain hobbies of mine, that I just cannot stand people being around me when I'm doing them. I find it insanely annoying and it feels as if people are peering over my shoulder watching every little thing I do. So, when I have the house to myself, I enjoy drawing on the computer--drawing certain things that are too embarrassing to draw when people are present--said drawings, when I'm not home alone, I'm really really strategic as to not let people look at what I'm drawing, except my monitor is in dead sight in the family room, so whatever. I'm always glancing around paranoid-like when I'm drawing those particular things when my family is around. My sister picks on me too much about "him" and I'm sick of it. Home alone is always best.
I also like to play the piano when I am home alone. Except, for this one, there are literally no exceptions for playing it when people around. I only play piano when I am home alone. Well, a piano can be heard all throughout the house, so... yeah. Especially if I'm trying to play songs related to someone I'm ashamed of and gdfhkslfdsklggh. So, I used to practice piano all the time with people around when I was younger, but I can no longer do that. My skill hasn't necessarily depleted, but I'm definitely slower to read music now because of the deprivation of constant practice. But whatever. I sometimes will play my mom's electric keyboard that is much quieter, when I'm in the house with other people, but nerm.
I sometimes sing, too. Sing what? It's a secret to everybody.
So, drawing and playing the piano are the primary two things I typically do when I'm home alone. Oh, and I also do things that I do regularly, like ZDing and playing videogames and whatnot...