Wintry sky

Tonight the temperature is set to plummet below zero but its been a  sunny day. 

Another cat has appeared on the scene. For the past couple of days we have heard  cat fights  or rather cat challenges in the garden and this morning I saw the culprit- a new young black male.  Oh dear! 
Quick search on google revealed it is possible to buy a battery operated cat repellant which emits a high pitched squeal  not audible to the human ear. Well, I have ordered one. 

Will it work? has anyone had experience of them?