Peltor Alert
True on the voice activation, though more correctly called voice attenuation. It doesn't actually get 'activated' though, rather 'deactivated'. Let me explain.
You turn voice attenuation on, or choose to leave it off. When you turn it on, you can turn it up.
Voice attenuation is an electronic circuit. It takes ambient sounds around you in through a small microphone and amplifies it into your earcups. You can turn it on to just barely perceptible, or crank it up so that a helicopter passing overhead sounds like its gonna land in your drop zone. Even filing a chain becomes a new experience. Kinda like a microscope for your ears.
The major benefit to voice attenuation is that you can be way up in a treetop and hear your ground guys commenting on the hot mom-babe across the street. That is, until you fire up your saw. When the ambient noise level goes higher than a certain decibel level, voice attenuation is automatically electronically deactivated - until the loud noise ceases, then back to as it was.
You can use the FM radio AND voice attenuation independently or simultaneously, meaning you can rock out, have your hearing protected (or ears kept warm) AND be acutely aware of all the sounds around you. If you're not bashful about singing in the trees, you can experience, bigger than life, just how bad your singing really is. If your singing sucks, just turn the radio up, V.A. off, sing loudly and ignore yourself.
Nickle metal hydride batteries are a must, and Peltor has developed a battery pack, removable, and rechargable through a wall socket.