It detects law-breaking beer fans, full of energy on drug (5,6)
I believe the answer is:
speed camera
'it detects law-breaking' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'beer fans full of energy on drug' is the wordplay.
'beer fans' becomes 'CAMRA' (Campaign for Real Ale).
'full of' is an insertion indicator.
'energy' becomes 'e' (physics symbol as in E=mcp).
'on' means one lot of letters go next to another.
'drug' becomes 'speed' (speed is a kind of drug).
'camra' going around 'e' is 'camera'.
'camera' after 'speed' is 'SPEED CAMERA'.
Can you help me to learn more?
(Other definitions for speed camera that I've seen before include "Roadside deterrent" , "What might capture" , "Roadside snapper" , "Roadside feature" , "flashy source of government income" .)