You would need to have one device be aware of the other (either directly or through a central server). Having that you can use GCM to push messages to the device, and once received, show the Toast
and vibrate.
I recommend you use Android notifications rather than Toast
and the vibration let it be what the user has configured to avoid being too intrusive.
You can start by reading up on GCM: http://developer.android.com/google/gcm/index.html