[Fyren]

You could use something like an Arduino to listen for the voltage change that happens when the bell rings/the circuit closes, which could then do whatever. If the iPhone and Arduino are always on the same wifi, you could give the iPhone a static IP and have it listening on a port the Arduino would send something to. If the phone should work anywhere, you could have a PC on the network listening instead, then it could send a push notification using Apple's service. You could probably also find some kind of wireless receiver/transmitter you could connect over COM/LPT/USB to the PC instead of having an Arduino, I guess.

You could try looking for a local enthusiast group for Arduinos/Raspberry Pis/other small devices like that for people to ask for advice.