Peugeot 208 Key Replacement
Peugeot 208 key replacement is best left to auto locksmiths with experience who have the proper equipment and know-how. They can create and program new keys quicker than a dealership and at a cheaper cost.
A dead coin battery is most likely to be the cause the reason why your key fob isn't locking or unlocking the doors. There are other reasons why the key may be malfunctioning.

Dead Coin Battery
A dead coin battery can stop your Peugeot 208 from locking or unlocking and won't start the engine. In this situation you'll have to employ the alternate method of starting described in your vehicle owner's manual.
Another reason why your 208 may not start is that the spark plugs are been worn down. Spark plugs are what ignite the fuel to start the engine. However they have a finite lifespan. If they aren't utilized enough they will eventually fail.
Luckily, there is an easy solution to this problem. Verify the voltage of your battery using a multimeter. If it's below 11.5 volts, then you need to replace it. It is also important to clean the contacts of the battery when it has corrosion. This can be done by lifting the rubber covers covering the two terminals of the battery and using a wire brush to remove any corroded components of the battery. You should then reconnect your cables to connect the positive and negative poles.
Water Damage
If your 208 does not start and the battery has not fallen flat, it is time to inspect the spark plugs. It could be that they are simply too dirty and don't spark. The spark plugs can be cleaned in a workshop.
Peugeot automobiles use a key with a transponder compatible with the immobiliser. This ensures only the correct key is able to turn the engine. If the chip inside the Peugeot key is damaged, it won't transmit the proper signal to the vehicle.
This is a common problem that can occur due to water damage. This is a typical issue in warmer climates where the vehicle is exposed to snow or rain. If this is the case, get in touch with a reputable locksmith who will have all the tools and equipment needed to modify the new key. new key for peugeot 207 will also have the latest technology and equipment needed to make the Peugeot 208 smart key. The process shouldn't take more than 15 minutes.
Contacts with the battery may be damaged.
Peugeot replaced the old transponder chips using a new type that uses electronic components that are mounted on a circuitboard. The new system is fantastic when it's new, however the circuit boards wear out over time and cease to function properly.
This can stop the immobiliser chip from working the immobiliser chip, causing your car not to start. Contact an Peugeot specialist, or a locksmith if this is the situation.
Another issue that is common is when the key fob battery is dying, this causes the key blade to stop getting into the lock. A car locksmith will replace the battery and then cut a new key blade for you. This is a simple solution.
Faulty Receiver Module
It could be that the receiver module is defective in the event that your Peugeot key fob doesn't work after being dropped on the floor, exposed to a sudden downpour or accidentally washed. The receiver is responsible for sending radio frequency signals to an on-board computer, which is responsible for controlling the centralized locking system of your Peugeot vehicle.
Rubber seals on the key fob block water from getting to the electronic chip. However, prolonged exposure to water could cause damage to these seals and the chip. Submerging the key fob in ocean water on the beach or throwing it into the water can be particularly damaging due to the high salt content.
The module will have to be replaced if your Peugeot spare key no longer works. This can only be done by a skilled auto locksmith or Peugeot specialist. As opposed to other cars, Peugeot keys are protected by an immobilizer that is unique and requires the correct programming to begin the engine. This is the reason that you should only trust an authorized Peugeot locksmith to create and program the replacement.
Computer malfunctioning on-board
The on-board computer of your Peugeot is responsible for various features in your car, including airbags and power windows. The on-board computer will display a code if something goes wrong. This code is stored inside the system and stays there until the problem is resolved. This can often mean that the on-board computers to be replaced.
One of the main causes of the light coming on is loose or corroded connectors in the airbag sensor. This could be due to wear and tear, aging, or exposure to moisture and salt. This issue needs to be dealt with as soon as you can, since an airbag that's malfunctioning could be dangerous in the event of an accident.
If your Peugeot is showing a card detected as not present error, the battery inside the key fob could be weak or dead. This will stop the key fob sending a signal to deactivate your vehicle's immobilizer. Try this by pressing the unlock key on the key fob and then trying to start your vehicle. If this does not work it is because the battery of the key is in need of replacement.