Attach a safety device (4)
I believe the answer is:
fuse
'safety device' is the definition.
(electronic safety device)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for fuse that I've seen before include "Melt; ignition device" , "circuit-breaker" , "'Blend, merge (4)'" , "Melt with heat" , "Electrical fitting" .)