lock button at the door handle

I never lock the car by pressing the door button. I use the buttons on the fob or the one on the door.

 

Sorry, I misread your post. I meant to day that I never use the lock rocker button on the inside of the door. I use frequently the one on the outside handle and it always has worked perfectly.

 

Are you touching the inside of the door handle while pushing the button? Try to keep your hand away from the door handle while reaching only with your thumb to push the lock button.

 

I too think that might be the problem. I Just went out and tried mine and it sometimes will not lock if you grab the handle and touch the little black unlock sensor on the inside of the handle when you push the square button. Most likely it dosen't know if you want it to lock or unlock. I also remember reading somewhere, sorry I can't remember where, that SKS might have a problem when the car is very wet. I haven't noticed this because it doesn't rain much in my part of Oregon.
Of course it's not a real serious problem because the button on the fob still works, and if all else fails there is the mechanical key.

 

I have noticed that when I wash the car with the fob in my pocket it will lock and unlock itself if I just lean on the door with out touching the button. I do hear the beeps when it does this. Do you see the inside light flash or hear the beep when you touch the button?

 

Nope. All kinds of rain, all sorts of cold. Just press the button w/o grasping the handle and it works 100% (Maine).

Lately though the wife has been somehow giving the prius a Grand Mal when she tries to open the liftback. If I open it it's OK, she does and it goes into a fit. It's something she's doing. Maybe not letting the Prius know she's a friendly before trying to open it. I do not know, just a guess.