The Smart Key broadcasts using it’s own 3V battery power supply. In order to save battery power, the Smart Key will only speak when spoken to (by the oscillators). If a Smart Key 3V battery does go dead, the car can still be opened using the key insert in the driver’s door, and started by inserting the Smart Key into the Smart key slot. However, wireless Smart Key functions will not work with a dead 3V battery. Replacement batteries (Camry PT# CR1632, Prius PT#CR2032) can be purchased from Walgreens and other stores.