wefranklin

I have a 2009 ES 350 For the past several months about one time in 10 when I return to the car it is unlocked. At first I was not 100% certain that I had locked the door. Now I am 100% certain that I push the lock button and it beeps once. So it is either not locking or coming unlocked by itself. I asked the dealer, more than once, he has no idea. What do I do? One of these times someone entered the car at night and stole items.
I did notice this posting from 2012, but no answer
"I have an Rx 350 lexus and I always lock my doors when I am home . Lately every time I go out both the front and back doors are unlocked . Does anyone know what may cause this . no one else in the house to unlock them . Could something in the house be causing them to unlock. Thought I would check here b4 calling service"