I HAVE ONE TELEPHONE LINE IN SERVICE WITH EXTENSIONS CONNECTED TO THE SINGLE
LINE.ENCLOSED IS A SCHEMATIC FOR A DEVICE THAT WILL LIGHT WHEN ANY INSTRUMENT
CONNECTED TO THE LINE IS TAKEN OFF HOOK.THIS GIVES WARNING THAT LINE IS BEING
USED. PCX.EXE IS SELF DISPLAYING SCHEMATIC FILE.
PARTS LIST
2 - 2.2M RESISTORS
1 - 330K RESISTOR
1 - 2N3906 TRANISTOR
1 - 33K RESISTOR
1 - 2N3904 TRANISTOR
1 - 220 OHM RESISTOR 
1 - LED
1 - 3 VOLT BATTERY SOURCE 2AA BATTERIES WILL WORK

PS 
 LED WILL LIGHT WHEN CIRCUIT IS COMPLETE,NOTHING IS WRONG. WITH PHONE LINE
 ATTACHED LIGHT WILL GO OUT.LED WILL LIGHT WHEN ANY INSTRUMENT IS TAKEN OFF 
 HOOK.REMEMBER PHONE LINE POLARITY.WOKKS GREAT ENJOY.