Son-in-law was packing the trunk of his Elantra (2009 or 10, not sure which) for a trip this morning and shut the trunk with the keys inside. Spare key was in unknown location. AAA unlocked the car doors but for some reason could not open the trunk. Normally you can access the trunk from the back seat but the seat release levers are also in the trunk. Every time he tried to release the trunk lid using the button, the alarm would sound. Disconnecting the battery and reconnecting did not reset the unauthorized entry condition.
I was able to get into the trunk far enough to reach the driver's side seat release by removing a 18 mm nut at the bottom corner of the seat-back. Even then the opening created was too small to crawl through so a long tool was needed to reach the release knob. Then I had to release the other side of the seat-back to make the opening large enough to remove the stuff he had packed to finally find the keys. What a PITA!