The demo key set is only meant for sample apps on our website (docs, blogs), useful for interactive online demos only and for trying out PubNub with the PubNub Debug Console.
Using the demo key set means that anyone subscribing to the same channel you are publishing to will receive those messages. The demo key set is throttled to prevent abuse, so any app using the demo keys may not behave as you would desire.
For development and testing of your apps, please register for a free account and use those keys.