How can I disable the unsafe volume warning?

At first I had the same problem as you but now when i plug the speakers it automatically lowers and limits the volume to 42% then I try to turn it up and the system don't let me do it. When I unplug the speakers and turn the volume up, I don't get any unsufe warning and the system let me put the volume at 100%. I don´t understand why it changed because I didn´t switch any definition.

I hope you can help me at least to put everything as it was at the first time.

I don't have this warning on any of my devices (Sony Vaio all-in-one PC, Dell Venue Pro 8 tablet, or Surface 2), so my guess is it is specific to a brand of audio driver.  Can I have you guys post back your audio card name (from Device Manager, press Win+X to get there) and let's see if there are any commonalities?

If I'm following what you are asking for, my audio brand is Realtek High Definition Audio --Driver version 6.0.1.7055. I have a Samsung laptop running Win 8.1. I updated the audio driver after upgrading to 8.1 per a notification from either Samsung or Realtek, I'm not sure which. It was then that I noticed the nanny warning. It is only when using the headphone plug for speakers or phones, not my built-in speakers.

I actually just discovered that as well -- it is when using the headphone plug.  I also found out that it is due to European law:

"Under the new rules, higher exposure levels are permitted, but the user must willingly select them after being presented with a warning of the risks and ways to avoid them. How the warnings are provided would be up to the manufacturer and how it displays on the device's screen. Under the old rules, only a warning in the instruction manual was required.

EU standards are not mandatory, however it 'de facto' becomes the industry norm," the European commission said. "Products meeting those standards are presumed safe -– otherwise manufacturers have to go through costly independent testing for products. The new safety standards will apply only to future products."

This same warning plagues Android with complaints and Apple products.

Further reading if so interested.

I guess that explains the mystery. Looks like writing your congressman might be more beneficial than writing to the manufacturer.

Thanks! I guess I'll just use the vol control on the external speakers and "allow" when it becomes necessary.

Looks like a Samasung thing. I first saw it on my Galaxy s3. Very annoying as I rarely plug headphones in to any device I own. I usually plug in a real speaker system, sometimes even concert sound systems (live audio engineer by trade). As soon as I can confirm, I'll update this post. My Samsung laptop, NP680Z5E-X01US does this no matter what I plug into the "headphone jack" and I don't even have to be running audio. From a fresh boot (startup) plug ANYTHING into the hole and try to turn up the volume. DOH! It stops at 39, removes any fullscreen, darks the display, and shows a stripe on top of everything else that says, "High volume can cause hearing loss Your ears are important. Turning up the volume past this point can cause hearing damage." With two options, "allow" and "don't allow" and the warning does not go away until you chose one.

-IF YOU OWN ANY SAMSUNG PRODUCT THAT DOES THIS, CALL 800-SAMSUNG AND COMPLAIN!!!! SAMSUNG WILL CONTINUE TO SCREW US, LIKE THIS, UNTIL WE DO.

Good luck.

Windows, do more, pay less. 

P.S. don't try to remove/rollback drivers on a Samsung computer, it will break it.