The Smarty Pants are only used in the episode Smarty Pants, though they appear in the final episode Who Will Be The Family Wizard. These pants are magical because wearing them gives the person superior knowledge on everything there is to know. Alex wears them and joins Harper's team for the Quiz Bowl since Harper's team needs one more participant.
The Smarty Pants have the appearance of loose-fitting leggings similar to flared pants that readjust to fit the wearer. They have a rainbow tye-dye like design to them accented by black sectioning.
Side effects from prolonged use of Smarty Pants are: (according to Justin) headache, nausea, rash, chronic giggling, belly button bubbles, "say it don't spray it" disease, tongue reversal, ear gas, sweaty knees, Picasso face, and problems with the bowel.
Later, when Alex steals the Smarty Pants, the Alarm mentions other side effects that include skeleton legs, smelly feet, yellow toes, flaky hair, oily lips, and scaly pits.
The Smarty Pants also seem to have an additional effect on the wearer causing them to be unable to answer a question asked (though this could be the "say it don't spray it" disease). Alex shows this in the latter half of the episode before Harper storms off.