Warning on vegetables that sends pulse racing (10)
I believe the answer is:
peashooter
'that sends pulse racing' is the definition.
(it launches peas or pulses into the air)
'warning on vegetables' is the wordplay.
'warning' becomes 'hooter' (type of siren).
'on' means one lot of letters go next to another.
'vegetables' becomes 'peas' (I've seen this before).
'hooter' put after 'peas' is 'PEASHOOTER'.
(Other definitions for peashooter that I've seen before include "child's toy" , "Toy weapon" , "Primitive weapon" , "Child's "gun"" .)