I've seen several references to this capability being available with Bluetooth 4.0/LE but I'm not sure where to start or how to implement it.
To be clear, I mean truly connectionless with only a receiver on one device and a transmitter on another. (or, more specifically a powerful transmitter on one device and a weak transmitter on the other, so the devices can be paired).
Something like the "Immediate Alert Service" sounds good, but is it too good to be true? It's difficult to tell over which layer a signal is 'connectionless'. Could anyone perhaps point to some documentation/implementation examples of this?
Take a look at the Core Spec V4.0 and do a search for "connectionless". There's details about using a connectionless L2CAP method.