Many modern vehicles are equipped with a keyless remote entry system (also called a remote car door lock) that allows the owner to remotely disarm an alarm system, unlock the vehicle doors, open the trunk and even start up the vehicle. The keyless remote entry system works by using a radio signal to activate a receiver in the vehicle that then sends a signal to the desired component. In order to transmit this signal, the remote requires electricity in the form of a small battery. Roughly every year, this battery will require replacing, which is a simple process.
Remove the remote unit from the key ring.
Use the coin to open the battery panel on the back of the unit, twisting counter-clockwise. A nickel is usually just the right size for the slot in the battery panel. Alternately, your remote unit may require a small Phillips screwdriver to remove screws that hold the plastic remote casing together. Remove the screws and split the remote casing apart to access the battery if this is the case.
Remove the battery panel, exposing the battery and circuit board beneath. A small, circular rubber ring may be placed on top of the battery itself, which keeps the battery snug in the compartment. This will need to be removed and set aside.
Remove the old battery from the battery compartment, noting which side is facing upward (this is usually the positive side of the battery). If the battery does not come out easily, use the flat-blade screwdriver to pry the battery loose. Avoid damaging the circuit board while removing the battery.
Examine the battery for numbers or letters indicating the type of replacement battery that is needed. Keyless entry remote batteries are generally flat and round 12-volt lithium batteries. Ensure that your replacement battery matches the battery you have removed from the remote unit.
Insert the new battery into the remote unit with the positive side facing up. Press the battery down firmly with your fingertip. The battery should fit snugly in the compartment. Place the circular rubber ring on top of the battery, if applicable.
Replace the battery panel cover and use the coin to twist it clockwise into place. Do not over-tighten the battery panel, as this may cause the plastic to crack.
Test the unit by pressing the the "Door Unlock" button while near the vehicle. If the remote unit does not unlock the vehicle doors, it may require reprogramming to link it with your car's receiver unit. The programming sequence commonly consists of a sequence of button-presses and ignition settings and is usually found within the owner's manual that came along with your vehicle or it can be found online (see Resources). However, certain vehicle years and models from manufacturers like Jaguar, Jeep and Volvo will require special equipment to be hooked up to the car. In these cases, the car should be taken to a dealership to reprogram the remote unit.
