Why would key ignition warning alarm go on whenever there is no key in the ignition, but door is open?

What is your question?

I parked my car in the garage, placed the SUV in park and turned off the key and removed it from the ignition. Whenever I opened my driver's door, the warning alarm began sounding as if the key was still in the ignition. I closed the door and the alarm stopped. I started the vehicle and backed it out of the garage and then pulled back into the garage, placing the vehicle in park, turning the key to the off position and removed the key. I opened my door and the warning alarm began sounding as if the key was still in ignition. Any advise???

How long has your 2013 GMC Terrain had this problem?

A couple of hours