Chloe rang regularly — a warning? (4)
I believe the answer is:
horn
'a warning?' is the definition.
(a horn might be used as a warning)
'chloe rang regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'chloe'+'rang'='chloerang'
The alternating letters of 'chloerang' are 'HORN'.
(Other definitions for horn that I've seen before include "Instrument - rhino's appendage" , "Musical instrument - antler" , "Cusp" , "Warning device on a vehicle" , "familiar to the matador?" .)