Warn head, showing watchfulness (9)
I believe the answer is:
alertness
'watchfulness' is the definition.
(synonyms)
'warn head' is the wordplay.
'warn' becomes 'alert' (alerting is a kind of warning).
'head' becomes 'ness' (type of geographical point).
'alert'+'ness'='ALERTNESS'
'showing' is the link.
(Other definitions for alertness that I've seen before include "Watchful attitude" , "State of vigilance and watchfulness" , "Showing attentive nature" , "Watchful state" , "It's needed to respond quickly to danger" .)