These are the type sold with 3D LCDs in Australian retailers. Shutter glasses are the most commonly used Active 3D glasses with the lenses actually small LCD screens.

When turned on, the lens darkens and the “shutters” close. This is synced with the screen displaying the 3D content.

As each different image is flashed the eye shutters alternate in time. Each eye sees a slightly different angle of the same image creating the 3D effect.