Do you use a single wire and half-duplex, or still both RX and TX ?
If you use a single wire, and you use polling by the central unit, you have to do something extra.
In that case, the other units must also disregard the answer by the polled unit.
Perhaps you can use an escape character, like the STX character for the central unit.
If the answer by the units never contain the STX character, and the central unit starts with STX, the units only have to wait for the STX and after that see if they are addressed.