This is NOT just for the Hyundai Sonata!!! If you have an auto with an electronic key fob and a starter button (no key is used to start the car)… You should absolutely make sure that you change the battery in both key fobs every 2 or 3 years. Why? Because a key fob with a dead battery is worse than losing your car keys. When it’s dead so are you 
Thanks for the tip. I hadn’t thought about that. We just got our first car without a key and only a fob. Can I assume you don’t get any sort of warning when the battery needs to be replaced?
Just goes to show you that every “solution” or “feature” brings another problem.
Most fobs have a physical key in the inside of fob for such emergencies. On my car there’s place to use the key underneath the cup holder, you have to remove the rubber mat on the bottom of the cup holder to access it. Also most new cars will display a message when your fob’s battery is low. It’s not really an issue.
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My Nissans show a low battery warning on the info screen when the fob gets low, also have a key inside the fob.
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That’s good to know. Thanks. The car in question is a Nissan. I guess I’ll need to read that part of the manual.
My 2009 RAV4 has a starter button and no hidden ignition for a key. If the key fob battery dies, you only need to touch the button with the toyota emblem side of the key fob to start the engine. I’d be very surprised if all other car makers don’t have a similar feature. A dead car battery is much more of an inconvenience than a dead fob battery.
It seems that GRoy needs to read the manual or at least have the dealer explain what to do if key fob battery dies.
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I wonder if this hidden key and ignition switch are documented int eh Hyundai owner’s manua?
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In the 2016 Sonata manual there is a hidden key (page 3-10), and a procedure to start the car if the smart key’s battery is dead (page 5-13).
The OP didn’t mention what year his car was, but it’s 2014 or newer, I would imagine that it would be the same.
Rhetorical question on my part, and thanks for the answer for the OPs sake.
I read the manual Mr. Volvo V70. I’m probably one of a VERY few individuals
that actually does. All it says is that if the fob malfunctions it might be
the battery, Then there are directions on how to change the battery. And
that’s it. No hidden key (the key in the fob is to lock the trunk and the
glove box when you leave the fob with a parking attendant.), no indication
on the dash, nothing.
On another note. That was a pretty smug response.
The instructions can be found in the manual under “Starting the Engine”;
NOTICE
If the battery is weak or the smart key does not work correctly, you can start the engine by inserting the smart key into the smart key holder. To eject the smart key from the smart key holder, press the smart key inward past the detent and then pull the key outward.
The smart key holder is in the center console.
Just out of curiosity, what year is your Sonata?
Its a 2014. I actually found out what to do on You Tube just now. There is something in the owner’s manual on p. 5-10. But it really isn’t clear what it’s referring to. You Tube made it much clearer.
What this really means is that a large number of auto owners will have no clue how to start the car if the battery in the key fob dies. The simple solution is to change the battery periodically. For those that are technologically savy go on You Tube.
I have a 2015 Jeep Cherokee Limited. Here is what the owner’s manual says about this situation: “In case the ignition switch does on change (start) with the push of a button, the RKE transmitter (Key Fob) may have a low or dead battery. In this situation, a back up method can be used to operate the ignition switch. Put the nose side (side opposite of the emergency key) of the Key Fob against the ENGINE START/STOP button and push to operate the ignition switch.”
My fob has an emergency key. Although the salesman indicated its primary use was as a valet key (to lock the glove box when using valet services) the owner’s manual can also be used to enter the vehicle (fortunately, there is a key hole in the driver’s door).
Just how do you use the owners manual in the drivers door key hole. Since owners manuals have become so big and heavy you could just heave it through a window to get in.
On our Acura, you get a warning message on the dash if the fob battery is low. Back to the manual to see if there is a hidden place for a key.
On my Mazda6 I get a low battery warning when my key fob battery is dying. If it dies I can touch the fob to the starter button and the car will still start. Battery replacement is pretty easy and there is an emergency key that will open the driver’s door.
That’s the way they all should be designed. But how many are??