I started getting this warning message after traveling over a bump in the road.
The problem was caused by a microswitch in the hatch lock assembly.
I removed the black plastic cover and slightly bent the microswitch lever away from the switch and the problem is gone.
Did not cost any money to fix.

I don't know how to post a picture of the microswitch showing the actuator arm that I bent with needle nose pliers. Can this be done?

This is a reply to Kris posting about "Key Detected in Vehicle" coming up when hitting a bump.
I too own a 2011 RX350 and have been seeing and having this issue since we owned the car (bought Used)
It is certainly related to hitting bumps or when going over a low place in the road.
I have taken it to the dealer and of course the problem never reveals itself and they look at me and wife and think we are crazy.
Well- I not only have a video of it happening on my phone - we have taken pictures of the message on the dash.
I cannot explain the exact cause yet and I am not convinced it has to do with back latch. The last time it was occurring it was happening very often- but dealer never saw it when it was in for oil change.
The other owners who have reported the problem are spot on with the symptoms and related causes (small bumps). This is definitely an issue with this vehicle but the exact cause and resolution is yet to be found.
I will stay on it.
Thanks
Todd

Hi! I encountered the same problem with my 2011 RX. Could you please send me o picture showing the microswitch that you adjusted?
newgruia@yahoo.com

Thanks,
Gruia

Yes ... look at the thumbnail row for attachment [paper clip] and picture.

Salim