It's not likely that all transmitters are transmitting all the time. Most jurisdictions have rules limiting such transmissions to intermittent transmissions spaced well apart.

In that scenario, building in both an ID byte and error checking is sufficient. The NEC protocol (used by X10 for ~40 years) works quite well. There's a PBP example at http://davehouston.org/PIC-RX-TX.TXT. If you need to send more than 2 payload bytes, you can extend this.

Transceivers that transmit only when queried also work quite well but at large increase in cost. The simple transmitter and receiver like those Bruce sells are inexpensive and available from many sources worldwide. http://davehouston.org/modules.htm