This paper presents 3motion, a novel 3D gesture interaction system consisting of a low-cost, lightweight hardware component and a general-purpose software development kit. The system provides gesture-based 3D interaction for situations where traditional tracking systems are too expensive or impractical due to the calibration and reference source requirements. The hardware component is built around a 3-axis linear accelerometer chip and transmits a continuous data stream to a host device via a wireless Bluetooth link. The software component receives this data and matches it against a library of 3D gestures to trigger actions. The system has been validated extensively with various example applications, including a “Battle of the Wizards” game, a character manipulation demonstrator, and a golf game implemented on a mobile phone.