The Aircurve for iPhone is a really cool idea — an amplifier that uses no power adapters or batteries. Instead, it amplifies the sound from the iPhone’s speaker using a coiled waveguide (think of an old-fashioned cheerleader megaphone wrapped around into a helix, and you’ve got the concept). The AirCurve is made of translucent polycarbonate so you can see the curving waveguide. There’s a pass-through slot so you can charge and sync your iPhone. The AirCurve is much less expensive than powered alternatives, selling for $19.99.