Sometimes, I come back to my IS350 and find the doors aren't locked though I'm sure I locked them.

Here's how I lock them. I park the car, turn off the engine, and press the door button to lock all doors. Freqently, I press the dash button to open the trunk before or after locking the doors. There may be passengers that take longer than me to close their door, but I wait for them to open their door before I press the lock button.

When I come back to the vehicle, I touch the door handle and all doors unlock. At times, there's no beep or sound it turns out the door was left unlocked.

Can you help me figure out what's happening here?

 

there was a thread a while back that sometimes in excessive rain caused doors to unlock because I had that issue sometimes. I couldn't figure out why

 

If you try locking the car but you can't, you should get a long beep alerting you. Is it only when you have opened the truck before locking?

 

from what you have written, it sounds like all the doors are not closed before you press the lock button. Wait until all the passengers close their doors, then press the lock button.

one way to test if all the doors are locked is to try the rear doors since they do not have sensors in the handles. If they are locked, then you know for sure the doors are locked (or look through the window and visually verify they are locked). If you come back later and they are unlocked, well then you have someone messing with you, or a genuine mystery on your hands.

we used to come home and one or more garage doors were open even though we were sure we closed them. Even went so far as to change the openers since they were old and didn't use rolling code technology. Turns out the nanny was letting the kid play with the spare remote while she was feeding her. Sometimes the simplest answers are the solution.

 

Now that's fricken funny!

 

Ah. I hadn't realized all the doors need to be closed before I can lock them. I bet that's it. A passenger still has a door open, I try to lock all the doors, and it doesn't work. I'll do some experiments with the doors and trunk to verify everything. Thanks!