Hidden Feature in Your Car Key You Won’t Find in the Manual — But Must Know

Look at the keys of today’s vehicles, and you’ll notice they’re no longer just simple metal blanks. Instead, they come as sleek fobs with buttons to control the central locking system, including locking and unlocking not just the doors but also the trunk. It doesn’t really matter whether you drive a Subaru, Toyota, or Volkswagen — factory keys are remarkably similar in design, something you can see for yourself.

But it’s not just their appearance that’s alike. The internal components and how they work are largely the same across brands. Many automakers have built hidden, “secret” functions into these keys that aren’t mentioned in most user manuals. So what exactly are we talking about? Here’s the trick.

As mentioned, modern car keys contain electronic components. If you were to open one up, the inside would typically look like this:

On the circuit board, there’s a power element — without it, the key simply won’t function. On roughly 90% of these keys, you’ll also see a small LED light that illuminates whenever a button is pressed.

Here’s the hidden part: if you press and hold, for example, the door unlock or trunk button, the LED starts to blink in a specific pattern. The blinking speed actually tells you something important. If the LED flashes several times per second, it means the battery is in good shape — essentially as good as new.

If it blinks only once or twice per second, the battery is starting to weaken, and it’s a good idea to have a replacement in your glove box just in case. If the LED flashes less than once per second, it’s a clear signal that the battery is near the end of its life and should be replaced immediately, otherwise it could fail at the worst possible moment.

Keep in mind this method works only for keys that have a button-press indicator LED. Most keys do, but not all, so it’s important to know your key type. Now you know a quick and simple way to check your key battery — a small trick every car owner should be aware of.