I had my truck open on its own once and set the alarm off. It just went off again last night in the garage (only the second time ever), and while I played with the trunk before leaving for work I don't know for sure if that was it this time. Hood sensor, hmm...

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2012 Honda Accord coupe V6 6-speed
7-1-08 to 1-16-12: 2003 BMW 540i Sport 6-speed