@Ben wrote:
I was thinking more for doors actually. I have casement windows (the crank out style), so contact sensors wouldn’t serve much of a purpose on them.
One more thought, depending on how close your casement panes align . . . you might be able to put the sensor on one and the magnet on the other, protecting both.
I did this with my sliding doors and passthrough windows. Where the they cross I put the sensor on one and the magnet on the other. Either moves it triggers.