A detached garage is safer in the sense that it doesn’t offer ready access to your house. But if your garage doesn’t adjoin your home, it could be a more inviting target for car thieves and drifters. After all, you aren’t as likely to hear an intrusion in a separate building. Overall, we’d say that merely keeping the door shut won’t be as big of a deterrent for a detached garage. Ideally, you’d add some sensors or cameras to make it easier to check on.