> http://cgi.ebay.com/APOLLO-DISCOVERY-58000-750-MULTI-SENSOR-SMOKE-DETECTO= R-/310200043689?cmd=3DViewItem&pt=3DBI_Security_Fire_Protection&hash=3Ditem= 48395d08a9 > - Only two wires, 3 connector for chained devices > - Two wires povide both power (very little is needed) and DataIn+/-, Data= Out+/- > - The resistor between DataIn+ and DataOut+ is less than 1 om > DataIn =A0 +--------------resistor-----------DataOut+ > DataIn =A0 negative-------------------------- negative The "resistor" is probably a fusible link that goes open circuit if incinerated or heated above a certain temperature, thus providing backup to anything else that may be there. Put a resistive loop across line at far end and if line goes O/C at monitoring end you should join Elvis asap. =A0=A0 =A0 =A0 =A0 Russell > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .