Let&#x27;s see if I can explain in a way that makes sense...<p>The person at the door has a keypad and an intercom (for talking or hearing prompts).<p>The intercom box calls the Twilio number and patches it live to the user at the door. This way anything the user presses on the keypad is received by the Twilio number.<p>Twilio, on their end, relays the input that they&#x27;re receiving from the user by POSTing payloads to a bot running on one of our cloud servers (just a regular little AWS server).<p>Our bot responds to Twilio&#x27;s POSTSs with TwiML commands (Twilio&#x27;s version of XML), which tells Twilio how to respond to the user at the door.<p>Twilio gets our instructions, and responds accordingly. In order to buzz someone into the door, Twilio just needs to emit a certain DTMF tone, and the callbox would unlock the door automatically.<p>Hope that all made sense.