'05 Prius "smart" key does not work in the auto - open, lock, start, etc mode. Is this a battery problem? The actual key when pulled out of the case, of course unlocks the doors and will start the car when in its case.
Yes, this sounds like a battery problem. Replace the battery in the remote, especially if it is the original. PA P
It is also possible that you disabled the Smart Key System. Check the little button under the steering wheel. Btw, this particular forum is for questions about the website, not questions about the Prius. Tom