Nice! I built the same thing for a gate at our vacation house at a lake. The home-owners have to register their mobile number so that if you call a certain number the gate opens based on number recognition. Every time new people were at the gate (deliveries, guests, renters) they would need to call the owner, who had to hang up and call the gate’s number.
I use twilio to make outbound calls to that number using my registered phonenumber. I put a Django app in front for home owners so they can add authorized phone numbers with a expiration date.
Whenever someone is a the gate they call a twilio number, my django app checks the validity, opens the gate by calling the gate’s number with my number as ID, plays back some welcome message “hello chris, welcome to…” and sends the owner a push notification that person X is en route.
Todo: add a feature to redirect an unknown number directly to the owner and open the gate after manual verification.