https://en.wikipedia.org/wiki/Amber_alert
Amber alert means something different than the author thinks ...
They wanted "red alert".
https://en.wikipedia.org/wiki/Red_Alert
This is just an idiom for denoting a high alert state.
Perhaps "Defcon 02" would be better understood?
Notice that that Wikipedia page links to a disambiguation page which links to https://en.wikipedia.org/wiki/BIKINI_state which may be more familiar to people in the UK than the meaning you are thinking of