1. A method comprising: using a detector or a sensor to detect a gunshot of a firearm; using a 3D sensor to sense an aim direction of the firearm substantially at the time of detecting the gunshot; using electronics or a processor to set a reference direction based, at least in part, on the aim direction; using the 3D sensor to sense subsequent aim directions of the firearm after the time of detecting the gunshot; and using the electronics or the processor to: compare any of the subsequent aim directions to the reference direction; measure recoil of the firearm, wherein the measuring is based, at least in part, on the comparing; and display and/or record the measured recoil of the firearm.