Comment by svnt

You probably need firmware and some major component modification, such as a display or battery, but not more than this, to pull it off. So at a minimum, two components, or perhaps one smart component such as a display.

It seems the model was the AP-900, not the AR-924, which used alkaline (ie removable) batteries, so a new theory is an EFP (explosively formed penetrator) manufactured into the device.

It appears the devices do not function on cell phone networks but instead on internal radio networks such as those used within industrial or medical settings.

Best guess is the displays because:

1) there is enough room for the EFP,

2) you could modify the component to trigger itself, meaning it doesn’t need coordination between any other parts of the device

3) there are a lot of injuries to the face reported — with a display you could trip on button push without needing access to the button, when people tend to be looking right at the EFP

4) in the videos the explosions look very directional