close imo
2 way device sends signal and listens to see if the signal has been acknowledged by the correct panel, if not sends another until acklowledged
1 way device sends signal, assumes its recieved and accepted and shuts down
Like shouting for your kids to check thay are ok while on holiday near a pool having a meal.
2 way you shout and expect an 'im fine' if you get one great back to the starter, no response you try again etc
1 way you shout and assume that all is ok with or without a response and get back to your starter.