How to Open a Mercedes Key Fob

There are a few different Mercedes key designs, but almost all follow the same basic idea:

• Remove the little metal emergency key.
• Use the gap you exposed to release or pry off the cover.
• Lift the cover or battery tray to get inside.

Below you’ll see how to open the two most common Mercedes fobs and a simple method that works for most new ones.

Step 1: Work Out Which Mercedes Key You Have

Take a look at your key and match it with one of these descriptions.

1. Chrome SmartKey (Newer Metal-Frame Style)

You likely have a Chrome SmartKey if:

• The key has a shiny silver / chrome frame around the outside.
• The shape is smooth and rounded, and it feels a bit heavier.
• There is a small metal key blade hidden inside that you can pull out with a tiny latch.

This style is common on many recent C-Class, E-Class, S-Class, and SUV models.

2. Plastic SmartKey (Older Style)

You likely have the older plastic SmartKey if:

• The whole body is mostly black plastic with no metal frame.
• The key feels lighter and a bit more “square”.
• The buttons are rubber or plastic, with lock, unlock, and panic symbols.
• There is still a hidden metal emergency key that slides out.

This design has been around for years and is still seen on many older Mercedes.

3. Very New Key Shapes

Some newest models have a slightly fresher design, but they still use the same basic structure:

• A release for the emergency key.
• A back cover that pops off once the key is out.

Even if your key doesn’t match the pictures you find online exactly, the steps below will still be very close.

Step 2: Basic Safety and Prep Before Opening the Fob

Before you start, keep these simple points in mind:

• Work on a clean surface (like a table or desk) so small parts do not roll away.
• Wash and dry your hands so you do not get dirt inside the key.
• If you are changing the battery, have the new coin cell ready so the fob is open for a short time.
• Try to use a plastic tool or the metal key itself to pry – a large screwdriver can mark the plastic.

Now you’re ready to open the fob itself.

How to Open a Chrome SmartKey (Newer Metal-Frame Key)

This is the most common “modern” Mercedes key. Opening it is mainly about using the emergency key to pop the back cover.

1. Remove the Emergency Key Blade

1. Hold the key fob so the Mercedes star logo faces up.
2. Look at the bottom end of the key (the end opposite the keyring loop).
3. Find the small slider or button there.
4. Press or slide this latch while pulling the metal key blade out of the fob.

Once the blade is out, you will see a slim opening where it used to sit.

2. Use the Key Blade to Release the Back Cover

1. Look down into the opening where the key blade came out.
   You should see a small slot or notch inside the plastic.
2. Insert the narrow end of the metal key into that slot.
3. Gently twist or lever the key as if you are turning a tiny handle.
   You do not need a lot of force – just a small twist.
4. You should feel or hear a soft click as the back cover pops loose.

If it does not move, check you are in the correct slot and try again with slightly more pressure, but do not force it so hard that the plastic bends.

3. Remove the Back Cover

1. Once the latch releases, use your fingers to pull the back cover off.
2. The cover usually slides or lifts away from the rest of the key shell.
3. Inside you will now see the coin battery and contacts.

At this point the fob is open. You can change the battery or inspect the inside if needed.

4. Closing the Chrome SmartKey Again

1. After you are done inside, line the back cover up with the key body.
2. Press it firmly and evenly until it clicks and sits flush all around.
3. Slide the metal emergency key back into its slot until it clicks into place.

Always test the buttons near your car after closing the fob to make sure it still works as expected.

How to Open a Plastic SmartKey (Older Style)

The older all-plastic SmartKey opens in a slightly different way. Instead of a removable back plate, it has a small pull-out battery tray.

1. Remove the Emergency Key

1. Hold the key with the buttons facing you.
2. Look at the end opposite the keyring – you will see a small latch or slider.
3. Press or slide this latch while pulling the metal key blade out of the fob.

You now see a slim rectangular opening where the key blade was stored.

2. Release the Battery Tray

1. Take the metal key blade you just removed.
2. Insert it horizontally into the opening where it came from.
3. Push it gently in the direction shown by the tiny arrows (usually away from the keyring end).
4. This motion will push the internal battery tray out from the side or back of the fob.

The tray may not fly out; it might just move a little so you can grab it with your fingers.

3. Pull Out the Tray and Access the Inside

1. Once the tray is partly out, use your fingers to pull it all the way out.
2. You will now see the coin batteries sitting in the tray.
3. This is the “inside” of the older SmartKey design.

From here you can replace the batteries or check for corrosion or dirt.

4. Close the Plastic SmartKey Again

1. After you finish, place the batteries back in the tray in the correct order.
2. Slide the tray back into the key fob until it clicks fully into place.
3. Reinsert the metal emergency key blade until it locks.

Again, test the key on your car once you are done to be sure everything is working.

How to Open Very New Mercedes Key Fobs (General Method)

If your key doesn’t quite match either style above, you can still use this simple method. Most newer fobs use a very similar layout.

General Steps

1. Find and remove the emergency key.
   There will be a small button or slider somewhere near one end.
   Press it, then pull the metal key blade out.
2. Look for a seam or notch.
   Where the key blade was, you will usually see a small notch, slot, or seam in the plastic.
3. Use the key blade as a lever.
   Insert the tip of the blade into that notch and gently twist until the back cover pops or lifts slightly.
4. Remove the cover.
   Use your fingers to remove the back cover or lift the small battery tray.
5. Access the battery or inside parts.
   Once open, you will see the coin battery and contacts. Handle them gently.
6. Close and test.
   Press the cover back in place, reinsert the emergency key, and test the fob near your car.

If anything feels stuck, pause and look for a second latch or a small arrow icon that shows the correct direction.

Common Problems When Opening a Mercedes Key and How to Handle Them

The Cover Won’t Pop Off

• Make sure you are putting the key blade into the correct slot or notch, not just any gap.
• Try a gentle twist instead of pushing straight in.
• If it still does not move, check your owner’s manual for a small diagram – some fobs release in a slightly different way.

You Are Worried About Breaking the Plastic

• Do not use huge metal tools; use the key blade or a small plastic pry tool.
• Apply steady, gentle pressure rather than fast, jerky force.
• If it feels wrong, stop and look again for a hidden latch or arrow marking.

The Key Still Does Not Work After Opening

• Check that the battery is the correct type and facing the right way.
• Make sure the cover or tray is pushed in fully and sits flush all around.
• Try your spare key.
  If the spare works fine but the opened key doesn’t, the fob itself may be damaged or need reprogramming.

In that case, it’s a good idea to visit a Mercedes dealer or a trusted specialist for testing.

Quick Summary

• Almost every Mercedes key fob opens by removing the emergency key first.
• Newer Chrome SmartKeys use the metal key blade to pop off a back cover.
• Older plastic SmartKeys use the blade to push out a battery tray.
• Very new keys follow the same basic pattern with small changes in shape.
• Use gentle pressure, watch for small slots and arrows, and always test the key near your car afterwards.

Once you have opened your Mercedes key fob one time, it becomes a quick and simple job you can repeat whenever you need to change the battery or check inside.