Lock the car, Open rear hatch to fetch a thing or two. Place keys in cargo area. Close the rear hatch, leaving keys in there.

Luckily never happened to me but I always carry both car keys when traveling out of town in any car.

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2017 Explorer 3.5 EcoBoost
2007 E83 X3 3.0si Crimson Red, Gray
2006 E53 X5 4.8is LeMans Blue, Beige (Gone)
2013 JK Unltd Sport Flame Red, Black(Gone)