The Stir Starter is the ideal stir plate to use when making a yeast starter.
Magnets - how do they work? We don't know, but here's a description straight from the inventor:
"This unit has two powerful NdFeB button magnets in the 12 VDC stir motor, which is controlled by a precision voltage regulator for easy speed adjustment. The RPMs of the drive motor are limited, so the motor will not "throw" the stir bar, yet it provides enough to get a good vortex going. A low voltage, plug-in wall transformer provides power to the unit. The black plastic case dimensions are 6" x 4" x 2", large enough to accomodate a 2000 mL flask as shown. A Teflon coated 1" x 5/16" stir bar is included. A "keeper" magnet is also supplied to lock the stir bar in place while the yeast is pitched, so the stir bar won't end up in your fermenter!"
This is the Stirstarter designed to hold one of the big 5 liter flasks. For a slightly smaller, more inexpensive stir plate, consider the 2L size Stirstarter!