With this mod, you can use 1 smart home window sensor for 2 windows/doors at once!
The Sensor is connected to one window, the magnet to the other, whenever one of them opens, the pair disconnects and sends "open".

On the pictures, I'm using it for my balcony door and the Window, to turn off the radiator if one is open. (and save money)
(hint: if you tilt both, it's seen as closed ^^')

It's designed for a 2.1 cm thick window edge, a total distance of 7.5 cm window to window and an about 4 cm high sensor (Aqara in this case).
But it should be easy to stretch and scale for other values.