NXT Magnetic Grabber

From the description:

"Eelco Klaver used a magnetic latching solenoid to build a magnetic grabber. The solenoid used is designed for low duty cycle applications where the solenoids energized position is needed for an extended period of time. The plunger latches magnetically in his basic position, until a negative electrical pulse is applied to allow the plunger to unlatch. Elco also build a mechanical guiding system to allow the plunger to reliable enter the hole of the solenoid."

Detailed information is here, at the bottom of the page via a PDF link.