So we have a strange issue. Our 2015 CX5 likes to illuminate the red key warning and sound the warning trill that the key has been removed from the vehicle. This happens with the engine running and only seems to trigger when a door is opened and then closed. This happens a lot as we start the car to get the ac blowing while we load up our toddler into his car seat. It doesn’t happen every time but we are up to about 80% reliability. The car doesn’t care how long the engine has been running, but seems to favor the front passenger door, but not exclusive. No codes are being stored, key is close to the start button, batteries are fresh, no door open warning illuminate, just the red key warning with the warning chime. Any ideas before we start selling limbs to have the dealer tell us they haven’t seen this before?

 

The FOB battery may need replacing, mine only lasted a year, which about normal.
RED Key warning and beep will sound when driver's door is open with vehicle running.
It's a warning to the driver that the ignition is not off.
Some of the key warning system settings are adjustable in most models.
I always keep the key on my person.
If none of this works, then the dealer will need to find the cause.

 

GMosesH Welcome to the forum