A fastener tool includes a motor, a drive mechanism connected to the motor and adapted to drive a piston, and a cylinder filled with high-pressure gas. The piston is accommodated in the cylinder and suitable for a reciprocating motion within the cylinder. The drive mechanism includes a blade fixed to the piston and a gear coupled to the motor. The gear contains a plurality of teeth adapted to engage with a plurality of lugs on the blade such that a rotation of the gear is transformed to a linear movement of the blade. The drive mechanism further includes a disengagement module which, within a period of a rotation cycle of the gear, is configured to prevent one of the plurality of teeth from unintentionally engaging with a misaligned one of the lugs.