Dig electronic signal that's useful for eating out (8)
I believe the answer is:
barbecue
'that's useful for eating out' is the definition.
(used for eating in the garden)
'dig electronic signal' is the wordplay.
'dig' becomes 'barb' (synonyms).
'electronic' becomes 'e' (as in e-mail or e-books).
'signal' becomes 'cue' (as in an actor's cue).
'barb'+'e'+'cue'='BARBECUE'
(Other definitions for barbecue that I've seen before include "Cuba beer for outdoor meat meal" , "Outdoor party (full of sizzle?)" , "Open-air party with roast meats etc" , "garden party" , "cook burgers, say" .)