The suggestion of using a 'dog's-whistle' is a good one, I have used the
same type of whistle for nearly 20 years and it has never failed to bring
back my feline from wherever it is that he happens to be hiding and the
advice to associate the sound of the whistle with a nice treat of some
description is spot-on.
(I did notice however that the so-called 'silent' whistles are not that
silent at all and you would be berated for blowing it at 1.00am but I
unscrewed my whistle and removed the 'barrel' and just blow through the
'reed-end' and all we hear is a slight rush of air - a bit like blowing out
forcefully yet the cat hears it as a very loud noise - even up to 500 yards
or more).
DS N7