Amazing function of device used by suspicious police (12)
I believe the answer is:
breathtaking
'amazing' is the definition.
(thesaurus)
'function of device used by suspicious police' is the wordplay.
I cannot really understand how this works, but
'by' could be 'at' and 'at' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for breathtaking that I've seen before include "Moving" , "way of getting air into the lungs" , "Awesome" , "if one is not one is dead?" , "Causing astonishment" .)