Since the device plugs into the headphone jack, ALL Nintendo DS sounds come through the earpiece. Since it's a mono and unpowered "speaker" this thing's not made to be a replacement for a real headphone set, and because it doesn't cover over your ear it doesn't do a good job of blocking out external sounds. But you can still hear the Nintendo DS audio through it in normal conditions...just don't expect to hear anyone if you're in loud locations like an airport.

When it's plugged in, the Nintendo DS system microphone becomes disabled and all sounds recorded will be through the headset's mic. We tested it with a few of the microphone-compatible games like Metroid Prime Hunters, Diddy Kong Racing, and Tony Hawk's Downhill Jam, and the recording quality is about the same if you were speaking right into the system's mic. If anything, it felt so good to finally talk using the DS without bringing the unit all the way up to your mouth, or hunching over to speak into the unit like an idiot.

The device will work with any game that uses the microphone on the system -- on the package it promotes Pokemon Diamond/Pearl, Nintendogs, Brain Age, and Metroid Prime Hunters, but any game that features "blowing" or voice recording will work. It will not let you voice chat in games that don't have that feature, so don't expect miracles.