I "modified" an ecolink Door & Window sensor, added a mercury switch. Works great.
https://www.amazon.com/gp/product/B01N5HB4U5/
More expensive but very easy.
Also this using a different Ecolink sensor:
I "modified" an ecolink Door & Window sensor, added a mercury switch. Works great.
https://www.amazon.com/gp/product/B01N5HB4U5/
More expensive but very easy.
Also this using a different Ecolink sensor: