Arson solved by sound detection (5)
I believe the answer is:
sonar
'sound detection' is the definition.
'arson solved' is the wordplay.
'solved' indicates an anagram (the anagram must be solved).
'arson' with letters rearranged gives 'SONAR'.
'by' acts as a link.
(Other definitions for sonar that I've seen before include "Echo-sounding device" , "Echo-sounding equipment" , "Underwater detector" , "Sub's navigation" , "Device for detecting objects used in arson" .)