Any of the X10 "eye" motion detectors will work to trigger Robo Dog.
Very true.
I just thought I would add that the Robo Dog (Rexx-10) is a strange hybrid between being compatible with X10's power line and RF control, and X10's wireless alarm.
Only the DM10a integrates in as an alarm type of sensor. By that I mean, only the DM10a needs to be "trained" (exchange security codes) and only the DM10a can be alarm-wise armed/disarmed.
For power line/RF, the Robo Dog is basically a transceiver, with unit 1 also assigned to trigger/stop a barking sequence. Any of the "eye" motion detectors work as power line/RF control for this.