Distress signals (6)
I believe the answer is:
flares
'distress signals' is the definition.
(a flare may be set off as a distress signal)
This is all the clue.
(Other definitions for flares that I've seen before include "Sudden brief bursts of bright light" , "Devices producing bright lights as signal" , "Wide-bottomed trousers" , "Bell-bottom trousers" , "Trousers with legs widening at the bottom" .)