My prius is turned off in the garage and it is still beeping very slowly. The keys are in the house. How do I make it stop?

disconnect the battery then reconnected an your problem should be fixed but let it sit for 10 minutes with the battery disconnected. you will possibly have to reprogram your time and radio stations because doing this will reset that.

That beep you hear that comes from under hood when car is off happens every 30 to 40 sec. There is a flashing symbol .It is telling you your starting battery is at 11 volts which means 50%. charged . Replace starting battery .