To open the cam - turn the lens as much as you can CCW,
it then comes out, then a little bit back.
Remove the screw on the bottom.
You may now put the two parts of the housing apart and
remove the switch assembly.
Try to unhook the clamp you can see to the left - after
this hurdle the cam is open.
Electronic devices are delicate and may
be damaged by electrical charges. Use appropriate equipment as soon as you
want to open the housing - and you are on your own, no warranty left
whatsoever (I assume)