Modern Toyota vehicles give you the option to use a Smart Key. The Smart Key can lock and unlock doors with the push of a button. It also acts as an antitheft device. The Smart Key transmits a signal that is picked up by the vehicle. The Smart Key's signal must match the vehicle's security code or the vehicle won't start. When the Smart Key's battery begins to wear down, the Toyota vehicle's digital display will give you a low battery warning. When a Smart Key's battery dies, it is much cheaper to replace the battery than the entire key fob.
Remove the standard key that is stored inside the Smart Key. To release it, press the latch on the side of the fob. You can now slide the standard key out of the fob.
Insert the end of the key into the small slot at the end of the Smart Key. Give the key a twist and the Smart Key fob will pop open.
Gently insert the end of the standard key under the edge of the circuit board that you exposed when you opened the fob. Lift up on the key to remove the circuit board. The battery is underneath.
Loosen each of the three clips holding the battery in place and remove the battery. Replace the battery with a fresh one. You can find the correct battery size at Radio Shack or at a pharmacy that carries hearing aid batteries.
Replace the circuit board and snap the top of the fob back into place.