Whether or not it's illegal in Maine to break out a car window in order to reach a dog on a hot day is kind of a gray area, but could get you arrested.
I asked Bangor's Animal Control Officer, Trisha Bruen last week, and she said it's kind of a 'gray area.' While it's technically not illegal to break the window, it's entirely possible the vehicle's owner could charge you with criminal mischief. Not only could you be charged for breaking in, but you could pay even more if the vehicle's owner sues you for damages. So she offered some suggestions on things you could do to help make sure the dog is healthy, and not suffering in the heat. Plus she had some tips for dog owners about how to know when a ride is not a good idea.