Sending a message or signal to a phone

I have an idea for a project but one feature I would like to add is the ability to send some kind of message to a phone (android) when an event happens. I see there are SIM shields for sending a proper text message but I don’t want to use a sim and mobile data. I’ll have an Ethernet connection or wifi. My first thought was to send a tweet with a specific @ or # then monitor that from the phone but it seems the twitter security protocols have changed and this is now quite tricky (is that the case?) . What other methods are there for doing this? I could just about write an android app if required but something standard at the phone end would be nice as I’m not that good at it. Any pointers on where to look or similar projects to copy or take bits from would be handy. Thanks sends a tweet from you wifi shield.
once you have it on the net, you can pretty much do what you want