is the doorbell pressed?
Another issue with polling is event stretching, a person can easily press and release a button before the node is polled so the node has to remember the press until it is polled.
I wouldn't say packets are sent in no time, I think that would violate various laws of physics, and you would be hearing from Einstein.
Can I build any kind of carrier-sense network, so that the nodes only use the network if it's free? Any guidelines on this?