Beeping noise on driver's door

Do you have the keys for the Prius with you when washing/drying?

If so, when you touch the door handle, you are locking the car signified by a beep.

 

As ePrius said, the SKS detects -something- it thinks is your hand on the door handle. Even the water can trigger it. It will lock and unlock, though once locked it won't stay unlocked unless you actually -open- a door (if you unlock but don't open a door within 20 sec they will relock).

If it bothers you leave the FOB 20-30 ft away, though I'm not sure this will prevent locking. It -will- prevent unlocking.
You could also try turning off the SKS system (little button under the steering wheel). I haven't tried this but it -should- have some effect.

 

If the car is running and you open the door or leave the car it beeps.

You may have forgot to shut the engine off

 

If the keys were in the car (bad move dude!) it's possible the car was warning you it won't lock the car with them in there. I suspect you were triggering the lock/unlock function. The only variable is why the car responded the way it did.

NEVER leave the keys in the car when washing it. Any car. It's too easy to lock it with all that messing around.

And yes, if you leave the car in "ready" without the FOB in the car the car will beep three times outside each time you close any door. It's possible the SKS system was triggering this.

 

The owner's manual details most of this. Water on the handle is sensed as a hand. Leave the key away from the car and it won't beep. (or lock)

 

I a few times left the car running and left the car with the keys in my pocket. An hour later I return and as soon as I get near the car it starts chirping