Could be protected first off with smoke sensor? (8)
I believe the answer is:
detector
'smoke sensor?' is the definition.
'could be protected first off' is the wordplay.
'could be' indicates an anagram.
'first off' means to remove the first letter.
'protected' with its first letter taken off is 'rotected'.
'rotected' anagrammed gives 'DETECTOR'.
'with' is the link.
(Other definitions for detector that I've seen before include "Device warning of, eg, smoke" , "Device for monitoring hazards" , "Sensor" , "Electronic device" .)