Wireless picks up origins of alien transmission — reading it could heat things up (8)
I believe the answer is:
radiator
'it could heat things up' is the definition.
(a radiator provides heat)
'wireless picks up origins of alien transmission reading' is the wordplay.
'wireless' becomes 'radio' (synonyms).
'picks up' means one lot of letters goes inside another.
'origins of' indicates taking the first letters.
'reading' becomes 'r' (one of the traditional three R's of education).
The initial letters of 'alien transmission' is 'at'.
'radio' placed around 'at' is 'radiato'.
'radiato'+'r'='RADIATOR'
(Other definitions for radiator that I've seen before include "It spreads heat as in house" , "Room warmer" , "Room heater" , "It spreads heat around room or cools engine" , "Aid or art, strangely, for the heater" .)