Hello TeslaIaint, I am a Zilog FAE and I woild like to help you with your PIR module needs. You noted that the Parallax module is 'unreliable', which could mean it misses motion events or it creates false motion events, or both. The ZMotion module is completely configurable so you can decide how sensitive you would like motion detection to be. Also, it includes an 8 pin 4kB MCU so you do not need to add an external one. There is a lot of information about the module on our web site at http://zilog.com/index.php?option=com_product&Itemid=26&task=docs&businessLine=147&parent_id=148&familyId=159&productId=ZEPIR0AA
We also have a forum at http://zilog.com/index.php?option=com_forum&Itemid=67
Our module kit is a good way to start evaluating our module. http://zilog.com/index.php?option=com_product&task=dev_tool_mpn&id=63&BL=147&familyId=159&mpn=ZEPIR0AAS02MODG&Device=ZEPIR0AA&puqs=b3B0aW9uPWNvbV9wcm9kdWN0JnRhc2s
Feel free to reply with questions or send me a private message if you like.
Thanks and Best Regards,
Zilog Field Applications Engineer