Genuine article installed by company that signals danger (4,5)
I believe the answer is:
fire alarm
'that signals danger' is the definition.
(a fire alarm alerts people to danger)
'genuine article installed by company' is the wordplay.
'genuine' becomes 'real' (associated in meaning).
'article' becomes 'a' (the indefinite article in English).
'installed by' means one lot of letters goes inside another.
'company' becomes 'firm' (I've seen this before).
'real'+'a'='reala'
'reala' put inside 'firm' is 'FIRE-ALARM'.
(Other definitions for fire alarm that I've seen before include "Safety equipment" , "Warning sound" , "Warner" , "It warns of smoke and flames" , "Warning device" .)