Garage door systems aren't much use if they can be opened easily with a hacked child's toy. Unfortunately, however, many garage door openers are vulnerable. This video can help you determine if yours is, and what to do if it is.
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First, a little background: security researcher Samy Kamkar found that garage doors that use an insecure "fixed code" system can be easily opened. He created a device called OpenSesame (from an old Mattel toy called the IM ME), which can try every possible combination for those garage doors in seconds.
Garage doors that don't use a "fixed code" wireless transmission but instead use a "rolling code" aren't vulnerable to this attack. In the video above, Kamkar shows you how to check your remote.
If you want to secure your garage, you'll have to change the opener, which costs a few hundred dollars but should be a relatively easy DIY project.