Double window sensors

How about this for low cost… Get a Z-Wave window sensor that has a pair of external contacts as well. Then buy some inexpensive magnetic window sensors and wire them all in series and attach to the external contacts on the z-wave sensor. If any of the Windows is opened, you’ll get a notification. You’ll just need to conceal the wires from the additional magnetic window sensors. You won’t necessarily know exactly which sash opened, but it is good enough for home security.

Here a discussion about one such device…