Abstract: An accessory device useful for any of training, compliance, safety, and accountability of individuals in the use of firearms. An embodiment comprises a circuit board and housing with a means for attaching the accessory to a firearm. The circuit board may comprise an inertial measurement unit (IMU), a GPS receiver, memory to store data, a means for transmitting data, and a microprocessor unit for controlling operations of the printed circuit board. The IMU may comprise a gyroscope, accelerometer, and magnetometer. The accessory can provide position and movement data of such accuracy as to disclose, after transmission and analysis, a firearm user's stability prior to and during discharge, how well the user managed recoil from the discharge, and how quickly the user returned to a starting position following discharge. A reviewer may also be able to discern movements such as those caused by a user's breathing or involuntary muscle contractions.