Might page sound horn and then make about-turn? (6)
I believe the answer is:
beeper
'might page' is the definition.
The definition suggests a singular noun which matches the answer.
'sound horn and then make about-turn?' is the wordplay.
I cannot quite see how this works, but
'sound' could be 'beep' (beep is a kind of sound) and 'beep' is located in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for beeper that I've seen before include "pager, perhaps" , "pager, eg" , "Emitter of electronic sound" , "electronic device" , "Electronic alarm" .)