I was going to post something about normally open vs normally closed reed switches, but then I remembered the last time I used reed switches was for an ammo clip. Magnet in the clip had to open the circuit so I needed the rarer NC switch.
For your Cortana chip you would use the common NO reed switch. It looks in the picture Ithica suggested is using a house window open sensor, so now I am curious to see the reed switch that you made.
My model version of the reed switch is a simple design
please refer to video for results