I shoot them with a "pea shooter", a cardboard pipe with a balloon attached to one end, loaded with dry lentils or rice. Stretching/charging and releasing the balloon makes a loud, directed thump noise, but by itself it's quickly ignored by pigeons. They need to be actually hit by the load to care. (BTW I can confirm, although quite violent, pigeons seemingly don't readily learn from this experience... They are really fucking stupid.)

They are adapted to city noise, honking, construction sites... Unless you use flash powder charges (like they do at airports), noise won't scare them reliably. And your neighbors, dogs and the cool birds won't be happy about frequent reality shattering explosions. The stuff they use at airports got enough power to blow off hands.

It sounds as if he had neighbours in the same building :-D

The neighbours probably won’t approve