Sensor for detecting whether a door is bolted or not?

I have an idea for an I.O.T project to detect whether or not a door is bolted (not just closed), but I'm struggling to choose an appropriate sensor. Additionally, I'd like it to be wireless (and battery operated) so there wouldn't be any cable management to deal with.

I did a quick prototype with an inductive proximity sensor which didn't work well, and looked into reed sensors. Any recommendations?