My chihuahua/Palm mix keeps running out of the house..?

So my chihuahua/palm mix Bailey Boo keeps running out the house lately, he almost got hit by a car 3 different times and the police showed up today and gave me a fine. He's 6 and a half years old. I would say a change in his moods of a little bit. We are all going thru a big change, moving soon. So, what gives? Is he unhappy? Got something? We love him and can't live without him. Any advice? Can i buy something that shocks him before he runs out the door? I'm at a loss, he's tiny, only 4 pounds, so we don't even know when he does this...currently, he's in timeout and looking like his new home which is his bed, attached to a leash. Feeling like an awful mama...any good help would be appreciated! Thank you!