I was washing my Sienna and each time water was touching the door sensor for the Smart Key system it would beep. I thought the sensor was hit or the remote was being used. So I did some research and reading the user manual and found this.
Page 46
- The doors may unlock or lock if a large amount of water splashes on the
door handle, such as in the rain or in a car wash when the electronic key
is within the effective range. (The doors will automatically be locked after
approximately 60 seconds if the doors are not opened and closed.
Page 47
* Note for locking the doors
- If the door handle becomes wet while the electronic key is within the
effective range, the door may lock and unlock repeatedly. Place the key
in a position 6 ft. (2 m) or more separate from the vehicle while the vehicle is being washed. (Take care to ensure that the key is not stolen.)
- If the electronic key is inside the vehicle and a door handle becomes wet
during a car wash, a message may be shown on the multi-information
display and a buzzer will sound outside the vehicle. To turn off the alarm,
lock all the doors.